It could hardly be described as one of the great games of the Premier League era but what it signified will long outlive the memory of the night itself. This morning, City lead the Premier League on goal difference with two games to play and they must now be the favourites to win their first title since 1968 if they can hold their nerve in their last two games against Newcastle and Queen's Park Rangers.
Vincent Kompany's goal, headed straight in from David Silva's corner in first-half injury-time, decided the game and possibly the title. But where were United's attempts on goal? There was a shot from Michael Carrick blocked by Kompany in the second minute and after that they simply never got close in a meaningful way. The champions faded as surely as that eight-point lead they held on 8 April.
At the start it was a 4-5-1 formation for United and they looked more than a little conservative in that system, with Rooney so isolated. As for City, they started hesitantly but grew bolder as they realised United were not prepared to come at them in any great numbers other than on the counter.
City looked most dangerous down their right. Samir Nasri early on wriggled between Paul Scholes and Park Ji-Sung, playing his first game since mid-March, and played Carlos Tevez in down the right channel.
There was an early setback for City when Kompany was given a soft booking by Andre Marriner for clipping Rooney's knee as he tried to get his leg around the striker to pinch the ball. .
With City on top, Sergio Aguero was allowed half a chance on 25 minutes. Rooney miscued a clearance, Pablo Zabaleta, in for Micah Richards at right-back, pushed the ball into the area and, via Joleon Lescott, it got to Aguero, whose volley missed.
Rooney was increasingly in the cold apart from one breakaway by Nani with five minutes of the first half left. Otherwise it was all City. As half-time neared, there was a strong run out of his own half by Tevez that took him away from Ryan Giggs and Park, and ultimately led to a corner.
Kompany's goal came after two City corners in succession. For the first David De Gea came off his line but could not get through a crowd of players. For the second it was his defenders who lost their way: David Silva's ball from the right was met firmly by Kompany at close range and De Gea had no chance. It looked like he was the responsibility of Chris Smalling but Rio Ferdinand will not enjoy watching that one again.