City have gone 35 years without winning a trophy but they will fancy their chances of doing exactly that now after seeing off their city rivals to make their first FA Cup final since 1981.
United had started by far the better of the two sides and twice should have taken the lead but Dimitar Berbatov fluffed his lines on both occassions, first firing at Joe Hart when clean through and then clearing the bar from point-blank range following a Nani cross into the danger area.
City looked overawed, but they gradually grew in stature and were by the better side by the time the first half drew to a close.
And seven minutes into the second period, as their dominance continued, Yaya Toure capitalised on a loose Michael Carrick pass to breeze past Nemanja Vidic and slot beneath Edwin van der Sar.
Hart tipped a Nani free-kick onto the bar as United briefly threatened a comeback, but Paul Scholes' dismissal, for a rash lunge on Pablo Zabaleta, left them with an uphill task in the final 18 minutes - one that, for once, they could not manage.
It means there will be no repeat of 1999 for United, who must concentrate on their bid for glory in the Premier League and Champions League.
There were unsavoury scenes at the end after Mario Balotelli rejoiced in front of the United fans, triggering a shoving match with Anderson and an angry reaction from Rio Ferdinand - who also squared up to City coach David Platt.
It was a world away from the opening few minutes, which saw United take an instant stranglehold on the contest.
Challenged to respond to the startling emergence of Javier Hernandez by his manager, the City goal first opened up for Berbatov when Carrick intercepted a Gareth Barry pass and began a fabulous one-touch move that involved Scholes and Park Ji-sung.
The Bulgarian found himself one-on-one with the outstanding Hart and went for the bottom corner. The England goalkeeper won.
United quickly retrieved possession and when Nani gave Zabaleta the slip, his low cross invited the close range finish. However, the man who had found the net for United 22 times this season scooped over on the stretch from inside the six-yard box.
Vidic turned an Antonio Valencia corner wide and Berbatov looped a far-post header just over as United continued to put the pressure on.
In fact it was half an hour in before City managed to push their opponents back and make them do some defending of their own.
Balotelli let fly with a rasping 30-yard drive that Van der Sar touched over and, had the Italian got on the end of Adam Johnson's corner shortly afterwards, United would have been in trouble.
As it was, the ball floated over the Italian to Joleon Lescott, who could not keep his first-time volley down.
Blues skipper Vincent Kompany curled a 20-yard effort just wide as half-time approached, then Balotelli failed to keep a near-post effort on target immediately after the break.
However, they were not about to let United off the hook in the manner Berbatov had done earlier.
Toure needed the assistance of a woeful attempt to find Scholes by Carrick after Van der Sar's kick had played his team into trouble. Once the Ivorian had been invited into the Red Devils' box, he finished in style, beating Van der Sar with a low shot through the veteran Dutchman's legs.
Now it was United's turn to wobble, just as they did in the Carling Cup semi-final 15 months ago.
On that occasion, Mancini failed to seize the initiative, settling for what he had in the first leg and watching his team swept aside in the second.
They didn't have Toure then, or David Silva.
It was the Spain star who crossed to present Lescott with another golden opportunity, which the England defender headed wide.
Given Ferguson compared the striker to Gary Lineker on Friday, it was not a surprise Javier Hernandez was asked to complete a salvage mission.
When the Mexican was introduced, United already had the free-kick that Hart pushed onto the bar as Nani went for the roof of City's net.
The comeback powers of Ferguson's team are the stuff of legend. Scholes' awful challenge on Zabaleta presented a challenge even they were up against it.
Carrick tried to atone for his blunder with a curling shot and Park attempted to steer a header towards goal but on neither occasion was Hart troubled to make the save.
As valiant as United's 10-men fought, City came closer to increasing their lead through Balotelli at the end.
It didn't matter and now the door to glory stands ajar for Mancini's men.