Yaya Toure shattered Manchester United's treble dream as Manchester City beat their bitter local rivals 1-0 to reach next month's FA Cup final.
Côte D'Ivoire midfielder Toure kept City on course for their first piece of silverware in 35 years after punishing a mistake by United midfielder Michael Carrick to settle a pulsating semi-final derby at Wembley after 52 minutes.
League leaders United, who last week advanced to the UEFA Champions League semi-finals, had Paul Scholes sent off for an ugly challenge on City defender Pablo Zabaleta as their dreams of repeating their famous 1999 treble were dashed.
City goalkeeper Joe Hart was ecstatic. "It means the world," he told ITV television. "The boys are over the moon, the fans are over the moon, the staff are over the moon. But nothing's been won yet."
City were worthy winners after raising their game in the second half to dominate their opponents. United might have taken the lead after an extraordinary passage of play on the quarter-hour mark which saw Dimitar Berbatov miss two glorious chances within the space of a minute.
City struggle early on
A wonderful passage of one-touch passing between Carrick, Scholes and Park Ji-Sung put Berbatov clear on goal only for England goalkeeper Hart to pull off a stunning close-range save to deny the Bulgarian.
Seconds later Portuguese winger Nani turned Zabaleta brilliantly on the left flank before racing to the byline and squaring for Berbatov, who scooped his shot over the bar from point-blank range under pressure from Aleksandar Kolarov.
With City struggling to gain a foothold, United enjoyed the lion's share of early possession and territory and had another chance to take the lead midway through the half when Nemanja Vidic flashed a glancing header just wide.
City had to wait until 32 minutes before their first meaningful effort on goal, Gareth Barry turning away from John O'Shea near the six-yard box but sending his shot into the side netting. Soon afterwards Mario Balotelli tested Edwin van der Sar with a ferocious long-range strike that the Dutch veteran turned over the crossbar.
Shortly before half-time City had alarm bells ringing again, captain Vincent Kompany whipping in a curling shot from the edge of the area that flew wide of the post by a matter of inches.
City's positive end to the first half was mirrored by a furious onslaught in the opening minutes of the second half, which saw Mancini's men threaten to over-run United at times. It was not long before City - looking far hungrier in the tackle and pressuring United relentlessly at every turn - took the lead.
Carrick mistake costs United
But City's 52nd-minute opener owed everything to a dreadful piece of play from Carrick. There was little danger as Carrick brought the ball out of defence until the midfielder rolled an aimless pass into the path of Toure, who surged into the penalty area, shrugged off the attentions of Vidic and shot past Van der Sar.
A few minutes later Adam Johnson forced another jittery stop from Van der Sar after cutting to the byline and lashing in a low cross that the United goalkeeper scrambled behind for a corner. Joleon Lescott then sent a glancing header flashing wide as City tightened their grip.
United forays into City territory were fewer and fewer, but Hart was pressed into action when Zabaleta fouled Park on the edge of the area to concede a free-kick. Nani's shot deflected off the wall but Hart managed to turn the Portugese winger's effort onto the bar.
An increasingly tense encounter saw Balotelli become the second City player to earn a caution when he clattered into Carrick. Referee Mike Dean's patience finally wore out on 72 minutes however, when Scholes was given a straight red for sinking his studs into Zabaleta's thigh. United rallied desperately but City were not to be denied.