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Nani's red card turned the game. It was a poor decision and Real took full advantage through Modric and Ronaldo.
Rio Ferdinand can expect to hear from UEFA after applauding right in the face of referee Cakir.
It's all over. United are out.
Time is almost up.
Real are playing out time, with the ball in United territory.
Vidic is in the right place to block another Ronaldo shot, before he shoots from a tight angle with De Gea equal to it.
SUPERB SAVE!!!! Van Persie's corner is met powerfully by Vidic but Lopez is equal to it and dives to his left to parry.
Corner for United.
Ronaldo breaks clear on the left but his powerful low shot is straight at De Gea.
Five added minutes will be played. Lopez, shock horror, is back on his feet.
Diego Lopez goes down after a tangle with Van Persie. There is absolutely nothing wrong with him. Blatant time-wasting. Pathetic.
OFF THE POST!!! Kaka escapes down the left and curls a shot against De Gea's upright, with the ball striking the back of the goalkeeper before he scrambles back to gather.
Obligatory yellow card for Pepe.
Final throw of the dice from Ferguson as Valencia is sent on for Rafael.
De Gea drops smartly to his right to keep out a shot from Ronaldo from inside the box.
Another good save from Lopez to deny Van Persie, before Rooney blazes over the bar from an excellent position.
GOOD SAVE FROM LOPEZ!! Quick short corner from Young finds Giggs and his cross is flicked towards goal by Carrick, only for the Real keeper to demonstrate excellent reflexes and parry to safety.
Welbeck's game is over and he makes way for Young.
Welbeck drills a shot against Ramos before Carrick smashes the follow-up over the bar. The home fans scream for a penalty, but the Real defender knew nothing about the ball striking his arm.
Ashley Young is about to come on.
Rooney attempts to find Evra as the left-back bursts forward, but his pass is over-hit.
Having taken the lead with two quick-fire goals, Real are now happy to soak up what United are throwing at them.
Welbeck's header is gathered by Diego Lopez as United, who now need to score twice, search for a way to rescue this match.
Time for Wayne Rooney. He replaces Cleverley.
Now Kaka is booked for pulling back Rafael.
Carrick goes into the book for something he said to referee Cakir.
Change for Real as Pepe comes on for the visitors in place of Ozil.
Crushing, devastating blow for United. Ozil and Higuain play a one-two and the striker drills a cross-shot across the face of goal where Ronaldo converts at the far post. No celebration, but that is scant consolation.
GOAL FOR REAL MADRID!!! Cristiano Ronaldo scores!!
Stunning, stunning strike from Modric. He picks the ball up outside the United box, moves away from Carrick and then powerfully curls a delicious shot beyond the despairing dive of De Gea and into the net via the inside of the post.
GOAL FOR REAL MADRID!!! Luka Modric levels!!
Ferguson and Giggs are urging the United fans to get behind their team and Old Trafford is responding in style.
Brief respite as United go on the attack with Robin van Persie's sweet low strike from outside the box gathered by Diego Lopez.
Modric rifles a low cross into the area where it strikes the back of Khedira and flies away to safety. United are living on the edge here.
United are being pinned back in their own half following Nani's dismissal. They need to push out or Real will surely level.
Modric takes over corner duties and nearly makes the breakthrough, finding Higuain under the bar, but Rafael does enough to clear the danger.
Ozil wastes it, yet again.
In all the mayhem, Mourinho has sent on Modric for Arbeloa. Real have a corner.
Ferguson is furious. Nani trudges off in disbelief. Ozil's free-kick is cleared and United now have to play for over 30 minutes with a man disadvantage.
Astonishing decision from referee Cuneyt Cakir. There is no doubt that Nani caught Arbeloa, but his eyes were on the ball and there was no deliberate intent to injure his opponent. Very, very poor decision in my opinion (for what that is worth).
RED CARD FOR NANI!!!
Nasty clash between Nani and Arbeloa as the United winger's high boot catches the Real man. They're both down, but Nani can expect a booking when he gets up.
Superb cross from out on the right by Higuan flies low across the centre of De Gea's six-yard box, but none of his Real team-mates were there to convert, much to the striker's frustration.
Another attempted shot from range by Ronaldo, another block from Nemanja Vidic.
Decent corner from Ozil towards Khedira, but Vidic clears. Ozil has a second chance to cross, but Rafael blocks.
Ronaldo earns a corner for Real.
Sir Alex Ferguson spoke at half-time about the need for United to take one of the chances they had been creating, and his side have clearly heeded those words.
Giggs and Rafael combine down the right and feed Welbeck, who loses the ball, before Van Persie's shot goes across goal. Varane dwells on the ball, allowing Nani to fire in a low cross which takes a flick off Welbeck and then Ramos can only divert into his own net.
GOAL FOR UNITED!!!! Ramos puts through his own net.
Now the Brazil international attempts to return the compliment to Ronaldo, but again the pass is overhit.
Ronaldo has the chance to run at United's defence before trying to slip a pass through to Kaka, but Vidic is across to clear.
Strap yourselves in again. United get the second half under way.
United's price to sneak a 1-0 win has been boosted to 5/1 at the break, while Welbeck remains 11/1 with Sky Bet to score the first goal.
Real need to score after the interval of United will progress to the quarter-finals on away goals, having found the net at Santiago Bernabeu three weeks ago.
Vidic's header against the post midway through the half was the closest either side have come to scoring. The loss of Di Maria could prove to be a big blow to Real. Ronaldo has been quiet so far and Welbeck is doing an excellent job nullifying the threat of Alonso.
Referee Cakir brings the half to a close.
Ronaldo shoots again from range but is way off target. One additional minute will be played. Mourinho has already seen enough.
Welbeck eventually steals the ball, but can only knock it out. Kaka comes on.
Kaka continues to warm up as United ease off and allow Real to keep possession.
Real, playing with 10 men, are knocking the ball around with ease.
Di Maria looks to have damaged his hamstring and is heading down the tunnel. Kaka will come on when the ball next goes out of play.
Di Maria is down and needs some treatment.
Superb ball from Giggs finds Welbeck on the edge of the Real box, but Varane gets in a great challenge.
Alonso, who is being well marshalled by Welbeck, attempts a raking cross-field pass, but only succeeds in putting the ball out of play.
Arbeloa goes into the book for a nasty challenge on Evra after a poor first touch.
Rafael goes to ground in the box under pressure from Ramos after being found by Giggs, but Cakir is not interested.
From the corner, Lopez is swiftly off his line in attempting to punch clear, but he only succeeds in flattening Vidic. The United man is OK to continue, if a little groggy.
CHANCE FOR UNITED!!! Van Persie works an opportunity by turning Varane with his stinging shot parried by Lopez, before the keeper is quickly up to deny Welbeck's follow up.
Real have the ball in the net, but the whistle had already gone for Ramos' challenge on Van Persie before Higuan rolled home.
De Gea comes out to deny Higuan from a tight angle. Another Real corner.
Key block from Carrick to cut out Higuan's low ball across the box towards Ronaldo after good play from Arbeloa. Real corner comes to nothing.
Ozil's corner is awful, but the ball comes back to him and his second cross loops off a Real head in the box and De Gea gathers.
Corner for Real as Rafael blocks Di Maria's attempted cross.
Rafael is put under pressure by Di Maria, with his route back to De Gea blocked by Higuan, but he is able to turn and clear his lines.
Superb ball from Khedira picks out Ronaldo in the United box, but Vidic is across to block as he prepares to shoot.
Ronaldo briefly gets away from Rafael as he cuts inside before unleashing a shot from some 30 yards out which strikes Vidic and United clear.
Nani has learned his lesson from previous corners and goes deep, with Van Persie getting his attempted overhead kick all wrong.
Superb play from Van Persie to release Welbeck. He breaks into the box and shoots, but Ramos slides in to concede a corner.
Khedira shoves Evra over on the United goalline to give away a needless free-kick.
A poor pass from Giggs finds Alonso and he then releases Ronaldo. Real keep the ball for a spell and probe the United defence but cannot find a way through.
Welbeck barely had time to react, even though he was facing an open goal from six yards, and may even have been flagged offside had the ball gone in.
OFF THE POST!!! Giggs' corner is met with a thumping header from Vidic which smacks the upright. The rebound strikes Welbeck, but then lands between the Real goalkeeper's legs as he lies prone on the line.
Great play from Giggs to force a corner out on the right after taking on Coentrao.
Evra goes into the book for hauling down Di Maria.
Nani's corner is utterly dismal and Real clear.
Great move from United. Ferdinand's raking pass finds Nani, who then exchanges passes with Welbeck before bursting into the area and forcing a corner.
Ozil is penalised for a foul on Carrick. United knock the ball about in defence, but then lose possession in attempting to feed Nani.
Nani's corner is swung into the box but Real clear and then earn a free-kick deep in their own half.
United threaten as Van Persie releases Welbeck. He is held up and Giggs then cross for Van Persie to fire towards goal and Ramos puts it out for a corner.
Van Persie's corner fails to beat the first defender at the near post.
Welbeck escapes down the left and then feeds Nani. His cross into the box is dangerous and forces Coentrao to head behind for a corner.
Good spell of possession from Real, but United's defence stands firm. Cleverley seems to be moving more freely.
First shot in anger, with Ozil finding Higuan on the edge of the box. He works a yard of space and attempts a curler into the top corner, but fires wide of the goal.
Cleverley is back up, but limping, after hurting himself in a tackle with Ronaldo.
Problem for United, with Tom Cleverley down in his own half and clutching his ankle. Referee Cakir stops play.
There's a rather frantic pace to the game at present, with neither team able to settle or keep possession for a spell.
Giggs is playing on the right flank in front of Rafael to offer extra protection against the threat of Ronaldo, with Nani on the left and Welbeck supporting Van Persie.
Corner to Real as Ozil picks out Di Maria, with Carrick cutting out his attempted cross. Di Maria's corner is headed away at the near post.
Carrick attempts a ball over the top from midfield to pick out Welbeck's burst into the box, but overhits it slightly and Diego Lopez is able to gather.
Giggs attempts to find Van Persie with a free-kick over the top, but the United striker had just strayed offside.
Ronaldo stands over the ball and then blasts his attempted free-kick straight into the wall. Huge cheer from the Old Trafford stands.
Free-kick to Real in an interesting position some 10 yards away from the left corner of United's area after Giggs brings down Coentrao.
De Gea's first touch sees him launch an attempted clearance straight into touch. Clearly a few nerves out there.
First touch for Nani, and he gives the ball away in his own half attempting a clever flick.
Shaky start from Ferdinand as he passes the ball straight to Ronaldo, but gets away with that early blunder.
Here we go. Real Madrid, wearing their green away kit, get us under way.
Ronaldo walks back out onto the Old Trafford surface he graced on so many occasions, with Mourinho making his way to the away dugout.
The two teams are in the tunnel and they enter the arena to a wall of noise.
There's a fantastic atmosphere in Old Trafford tonight with kick-off now a mere five minutes away.
Chris Dunkerley, from Pittsburgh USA, pulls no punches as he writes: "That team Ferguson picked is a disgrace. How can he reward Nani for his indifferent form. Rooney will leave in the summer, he cannot keep being treated like this. This is not a team to win, and Fergie will have cost us any chance to progress in this competition. Madrid to win 3-1."
If you missed the team news earlier in the evening (where have you been?) Wayne Rooney is on the bench and Ryan Giggs makes his 1,000th senior career appearance for Manchester United. Full line-ups and formations for both sides can be found by clicking the 'Teams' tab at the top of this commentary.
Tonight's referee is Cuneyt Cakir from Turkey.
Sir Alex Ferguson has been explaining his decision to leave out Rooney: "Wayne needs a game or two. He will probably come on in the second half and win the game for us, hopefully."
Pete Shields, a Newcastle fan, writes: "I think it is always foolish to try to second guess Sir Alex Ferguson. He is the best in the business and I hope his experience pays off. I can, though, see him using Young and Rooney at some stage and possibly even Hernandez. I guess it will all be about keeping Ronaldo fairly quiet - not easy but United have the players to do it.Good luck Man U."
And Liam adds: "What a game it should be tonight! Disappointed there's no Rooney, but he played 90 v Norwich so no surprise! 2-1 United!"
Albert Myint has been in touch on Twitter to say: "I think Sir Alex has made a good choice putting in Giggs and leaving out Rooney.... Giggs will add plenty of experience."
Christopher Peddie writes: "Can't believe Fergie hasn't started with Rooney. You need your strongest XI against Real. Just hope we don't end up rueing the team selection come 10pm! Don't think I can watch!! Think it's gonna be a 3-2 either way. I just hope we don't leave it till it's too late before making changes."
Real may be off the pace in La Liga, but back-to-back victories over Barcelona - one in the Copa del Rey, the second in Liga action - are not to be sniffed at.
United go into this match in superb form, with Ferguson's side having won nine of their last 10 in the Premier League to open up a 12-point lead over Manchester City.
Following Rooney's shock omission, Sky Bet have boosted Danny Welbeck's price to score first again to 11/1, while Gonzalo Higuain is 8/1 to beat him to it. There are also a range of Cristiano Ronaldo specials on offer, including the Real Madrid man to score a direct free-kick at 9/1. Other match specials include either manager to be sent to the stands (7/1).
Our friends at Sky Bet have a host of markets on tonight's encounter. Manchester United can be backed at 19/10, Real Madrid are a 13/10 shot and the draw is on offer at 13/5.
Scott, from San Antonio, Texas, writes: "Lots of United supporters scratching their heads. My belief is simple, what Sir Alex sees is what he sees. There is a reason for it. Probably a 4-3-3 with Nani and Welbeck as wing forwards. Or they can go 4-5-1 easily without having to alter anything. Makes sense. This decision separates the real supporter from the bandwagon supporter. This makes sense, crazy to say."
Opta stat No.4: Sir Alex Ferguson has only won twice in his 15 competitive encounters against Jose Mourinho (seven draws, six defeats).
Opta stat No.3: Real Madrid have had the most shots in this season's Champions League with 154 - that's 56 more than Manchester Utd.
Opta stat No.2: Real Madrid have only failed to score once in their last 32 Champions League games, against Barcelona at Santiago Bernabeu in April 2011.
Opta stat No.1: The two Champions League encounters between Manchester United and Real Madrid at Old Trafford have produced 12 goals.
Time for a few pre-match stats from our friends at Opta.
Benjamin March says: "I've Nani in a first goal sweepstake, but my shout is 2-1: CR7 to score first, RvP and Rooney (when he comes on) for United."
Alex Bullions has been in touch via Twitter to say: "Real Madrid's form is too good to beat especially on this stage. Real 3-1 win for me."
Aiden says: "Well you could argue that Rooney should play but you could also argue that he has him as a back-up plan. I don't think the midfield is as strong as it should be either."
Rob Gaskell writes: "Smart move by Fergie for two reasons - Rooney tends to drop central and becoming overbearing when asked to play deep (leave that for Carrick) and Giggs' 1,000th means the spotlight for the United fans is taken off Ronaldo. 'No legend like Giggs and he's playing for us' is the message there."
Barry Lee, from South Carolina, says: "Can't believe Rooney is not in there. Big mistake."
Simon Elliott reckons: "He surprised us with the team for the away game, he's done it again tonight with no Rooney. But Fergie knows his players. Looks like he is aiming to out gun Real Madrid accepting we will concede goals tonight. 3-2 United!"
Rafee Ahmed writes: "What has Sir Alex done? Without Wayne Rooney Man Utd have no chance. RVP and Rooney would have destroyed Real Madrid's defence...Shocked!!"
Fair to say there has been plenty of feedback on the United starting XI! Dan Walker is first to have his say: "The starting line-up is not what I had hoped for. Leaving out Evans and Rooney seem like bold choices with Vidic and Giggs coming in. Evans is arguably our best defender at the moment and Giggs' legs could tire in an energetic game. Hope to see Kagawa come on at some point and show more of his class like at the weekend. Backing a close 2-1 to United."
So the teams are in. Ryan Giggs makes his 1,000th career appearance, but there is no place in the starting XI for Wayne Rooney. What do you make of that, United fans?
Real Madrid: Lopez; Arbeloa, Varane, Ramos, Coentrao; Khedira, Alonso; Di Maria, Ozil, Ronaldo; Higuan. Subs: Adan, Pepe, Kaka, Benzema, Albiol, Modric, Callejon.
Man Utd: De Gea; Rafael, Vidic, Ferdinand, Evra; Carrick, Cleverley, Nani, Giggs, Welbeck; Van Persie. Subs: Lindegaard, Evans, Valencia, Rooney, Hernandez, Young, Kagawa.
Let me know where you're following the game, give me your score predictions and feel free to get anything else off your chest (preferably related to tonight's match).
If you want to have your say on tonight's match, then drop me a line to firstname.lastname@example.org or via Twitter @skysportsrobp and I'll publish a selection of the best prior to kick-off.
And there is also the latest head-to-head meeting between two of the games most successful coaches, Ferguson and Jose Mourinho. There is a mutual respect between the duo and there are many who feel the Portuguese could be the man to finally replace the long-serving Scot when he eventually decides to step aside.
Next, there is the landmark of 1,000 career appearances on the horizon for Manchester United's Ryan Giggs. The Welsh veteran, who signed a new one-year deal with United last Friday, was rested for Saturday's victory over Norwich and Sir Alex Ferguson has confirmed he will be involved tonight.
To begin with, there is the return of Ronaldo to his former home of Old Trafford for the first time. The Portuguese superstar spent six years with the Red Devils from 2003 to 2009 before his £80million move to Real.
On top of the undeniable magnitude of the match, there are a number of interesting sub-plots to this evening's encounter.
The last-16 tie between two of Europe's greatest clubs is perfectly poised following a 1-1 draw in the first leg at Santiago Bernabeu, when Danny Welbeck's opener was cancelled out by Cristiano Ronaldo.
Good evening and welcome to our live and interactive text commentary on tonight's huge UEFA Champions League showdown between Manchester United and Real Madrid.