Having unluckily been two down at the break, Sir Alex Ferguson's side came from behind through the Portuguese winger to snatch a derby victory that will live long in the memory
United made the best start, forcing a corner in the first five minutes from which Chris Smalling had a chance to bundle the ball over the line but his effort was blocked on the line.
The first signs of derby animosity showed after twenty minutes when Edin Dzeko and Anderson clashed over a tackle by the Bosnian forward, each earning a yellow card for their angry reactions.
Soon after, Micah Richards was lucky only to receive a yellow for a wayward lunge on debutant Ashley Young just outside the penalty area, and Wayne Rooney went close with the free-kick, curling just over the far post from a tight angle.
City finally created a chance on the half-hour mark, with a slick passing move. Yaya Toure surged forward to supply David Silva, who played a sumptuous through-pass for the advancing James Milner, who, under pressure from two defenders, had his shot deflected past the far post, but a goal kick was harshly given.
Another deflection later saved City’s blushes as Dzeko, part of a wall defending a direct free-kick, saw Nani’s shot bounce off his knee and fly inches past the post.
But against the run of play, City drew first blood when Joleon Lescott evaded his marker to meet Silva’s delightful in-swinging free-kick to place a precision header into the top corner.
And with the momentum suddenly theirs, the Citizens immediately pushed forward again, and when Patrice Evra brought Milner down there were suggestions that he had denied a goalscoring opportunity, but only a yellow was awarded and Silva squandered the set-piece.
Full of confidence after the breakthrough, City sent their neighbours into shock just on the stroke of half-time when a powerful swerving shot from Dzeko flew past David de Gea into the net from some way out, although the young Spanish keeper was late to get down and really should have saved.
Sir Alex Ferguson reacted by injecting youth into the team at half-time, with Phil Jones, Jonny Evans and Tom Cleverley all replacing more experienced heads at the break.
It seemed to work, with United again starting the half much brighter, and were rewarded quickly when Smalling pulled off a stylish mid-air finish, having been given a worrying amount of space in the City box to reach Young’s free-kick.
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And just minutes later, with City in shellshock, a great team move from United saw them draw level. Cleverley, Welbeck and Rooney were all involved with a devastating series of quick passes on the edge of the box that loosed Nani for a decisive finish, giving the Red Devils their just reward for a barnstorming start to the second period.
United were firmly on top, and with City trying to get forward to re-establish momentum, Ferguson’s side looked dangerous on the counter. Lescott made a great tackle halfway through the second period to rob the ball from an ominously-approaching Rooney.
But with the league champions not pressing their advantage home for a winner, City began to recover their confidence, Richards nearly sneaking a late winner with a powerful header from a far-post corner, but de Gea reacted well to keep it out.
Dzeko and Nani also had late chances saved at either end but just as it seemed that the game was destined for penalties, a catastrophic error from Kompany allowed Nani to burst through one-on-one with Hart in the final minute of stoppage time, and he made no mistake, rounding the keeper to slot in a simple, and deserved, winner.