There has been much discussion of Manchester United's departed or injured defenders, but far less of Michael Carrick. Will his return to fitness cause notable improvement?
Arsenal fans have been sucked back into believing Wenger can bring the glory years back after beating Borussia Dortmund. Plus, more on Liverpool's worrying decline...
"Nothing is unthinkable. It has happened to 99 per cent of all the big clubs in Europe [missing out on the group stage] but we want to be in there. We think we have the potential to do it. The task is clear, and we know we can do it. So let's do it."
Arsene Wenger's pre-match message was clear and firm - Besiktas presented themselves as the slipperiest of banana skins. This was a night on which only the outcome would matter.
Unfortunately, whilst Wenger may claim that only the result is king, it was also an evening on which it felt like his very ethos was being judged. The (perhaps nonsensical) rumours that Nikola Zigic would be the answer to supporters' intense frustrations over the perceived lack of back-up to the injured Olivier Giroud led to an atmosphere of 'go on, prove us wrong' at the Emirates. The jury is probably still out.
Wenger picked the same false nine formation (with Sanchez as the central forward) that fell flat on its face at Goodison just four days previously. It might seem knee-jerk in the extreme, but a second chance felt strangely like last chance, with five days of the window remaining to change plans should disaster occur.
Perhaps it was no surprise that the match seemed to sit on a knife edge, qualification confirmed only with screams of relieved joy from supporters that greeted the final whistle. For Wenger, there was a double fist pump in celebration - that's about as animated as it gets. Whatever the expectations of tension beforehand, little had prepared supporters for the torrid shredding of nerves they endured.
Arsenal started brightly, but in the first period suffered from a similar issue to Saturday, plenty of passing and creativity until the ball reached the final third, then very little thereafter. Sanchez had seven fewer touches than any other Arsenal player before half-time, increasingly forced to drift wide and towards his own goal to pick up the ball, too often leaving a noticeably vacant penalty area. Such a style rather limits the method of chance creation, forcing intricacy over directness - it is exactly this restriction that a target man option (no, not Zigic) would provide.
The goal, when it came, was a blend of both accident and design. Jack Wilshere and Mesut Ozil exchanged passes on the edge of the box, and when Wilshere miscontrolled the return ball it fell into the path of Sanchez, who guided it under the on-rushing Tolga Zengin. Sanchez only scored three Champions League goals in 24 matches for Barcelona, but opened his Arsenal account on the stroke of half-time.
Predictably, the goal both caused relief and forced Besiktas to attack, creating huge gaps in their defence. Arsenal may have their flaws, but there are few sides better set up for counter-attacking at pace, with Alex Oxlade-Chamberlain, Ozil and Sanchez able to surge forward on the break. Oxlade-Chamberlain, Cazorla and Mathieu Debuchy were guilty of missing presentable chances to end the tie as a contest. The Frenchman's greater guilt was still to come.
Questions over Debuchy's discipline and decision-making rose their head after his first season at Newcastle, when he was sent off for a wild challenge on Philippe Coutinho in May 2013. He received eight Premier League bookings last season, supplemented by a red card for a two-footed lunge on Claudio Yacob in January.
"He's a winner," was Alan Pardew's explanation of Debuchy's often tempestuous nature. "He gets emotionally involved in games. Winners will sometimes do frustrating things, because they want to win."
Whilst Pardew's sentiment may be intended as complimentary, Debuchy's ill-discipline could have cost Arsenal dear. His first-half bodycheck (for which you can read shoulder into face) on Olcay Sahan is the type of challenge that at some point will be clamped down on by UEFA - dangerous, calculated and cynical. It was worthy of the booking he received, and the Frenchman was then extremely fortunate to not concede a penalty for a challenge on Mustafa Pektemek. Replays showed that Pektemek got to the ball just before Debuchy slid in.
When his red card finally came, it was as debatable as Aaron Ramsey's just eight days previously, but Debuchy appeared to tug back Pektemek before diving in to win the ball. His reaction to referee Pedro Proenca indicated his frustration, but Debuchy had put his side through unnecessary strife. He owes his teammates an apology.
Through some frantic defending and an inexplicably missed header from Demba Ba, Arsenal survived, and will take their place in pot one of UEFA's Group Stage draw on Thursday. It is through consistency rather than glory that they sit in such elite company: Arsenal will partake in their 17th consecutive season of Champions League group stage football, a run matched only by Real Madrid.
A late winner against Crystal Palace to blow away potential opening day gloom, a last-minute equaliser against Everton and then hanging on with ten men against a side that finished third in UEFA's 12th-ranked league. Whatever the deliberations over Wenger's need for a new forward or talk of different attacking systems, there is one overarching trend that screams out so far this season: this Arsenal side aren't making life easy for themselves.
With post-match confirmation that Giroud will be out until January, things don't promise to run smoothly any time soon. As ever, this is a club that seems to give with one hand, and take with the other.
Daniel Storey - Follow him on Twitter
While we Gooners may have some reasons to be cheerful, there are without doubt some more nervous times ahead. A talented young & committed GK, who appears to give his defence very limited confidence. Our BFG, is looking more like Senderos with every game. Midfield can offer much, but need to control games better. A striker?, Sanogo might one day have it, but it's not going to be this year I fear. What do we mere supporters know, we must continue to hope that 'Arsene knows'- bailey