At half-time Manchester United boss Sir Alex Ferguson would have been forgiven for thinking that history was about to repeat itself, as despite dominating the early exchanges, as they did against Manchester City in the FA Cup semi-final last season, it was their fierce rivals who lead at the break.
On 37 minutes Joleon Lescott gave City the lead when he glanced in David Silva's cross as the Reds defence hesitated. In time added on at the end of the first-half Edin Dzeko caught out David De Gea with long-range effort which appeared to deceive the Spanish keeper in flight.
The second-half was all United who refused to let their opponents settle. Within 12 minutes of the restart United had hauled themselves level.
Ashley Young flighted in a free kick and Chris Smalling arrived unmarked to guide the ball past Joe Hart. Then came a sublime team effort from the Reds which bewildered the City defence as a swift interchange of passes on the edge of the area ended with Nani chipping over Hart from close range.
United still pressed but just as it seemed penalties would be needed to decide the outcome Nani showed determination to claim the decider.
Edwin Dzeko just moments before the winner failed to connect with a free header which would have won the game for the Blue half of Manchester, and as the ball was cleared up-field Nani robbed a hesitant Vincent Kompany on the half-way line before racing clear and rounding Hart to stroke the ball into an empty net.
Referee: Phil Dowd
Man City scorers: Lescott 38, Dzeko 45
Man Utd scorers: Smalling 51, Nani 57, 94
02 Richards (yellow card)
13 Kolarov (yellow card) (Clichy 73)
07 Milner (yellow card) (Johnson 67)
34 De Jong
42 Y Toure (yellow card)
10 Dzeko (yellow card)
45 Balotelli (Barry 59)
15 Stefan Savic,
01 De Gea
03 Evra (yellow card) (Rafael 71)
05 Ferdinand (P Jones 46)
15 Vidic (Evans 46)
08 Anderson (yellow card)
16 Carrick (Cleverley 46)
19 Welbeck (Berbatov 89)
04 P Jones,
13 Park Ji-Sung,