Rooney got the first of seven goals at Old Trafford [AFP] Ryan Giggs produced a virtuoso performance to dig his bungling Manchester United teammates out of a hole and set up Michael Owen for a 96th-minute winner in a 4-3 derby thriller at Old Trafford.
Craig Bellamy looked to have give a battling Manchester City a point when he latched onto an awful flick from United defender Rio Ferdinand to run half the length of the pitch and score past Ben Foster seconds before the end of normal time.
But as the clock ticked well past the alloted four minutes' injury time, Giggs stroked a beautiful through-ball for substitute Owen to dink over the unfortunate Shay Given in the City goal.
Given will be cursing his luck after producing a string of saves in the second half to keep out United, who bombarded the City area with crosses from Welsh wizard Giggs.
It followed a first half in which Wayne Rooney bagged an early opener with a jink through a crowded box and low finish.
But England keeper Foster handed City an equaliser when he failed to clear under pressure from the returning Carlos Tevez.
Tevez silenced the boos ringing round Old Trafford at his every touch as he set up Gareth Barry for a cool finish as Foster scrabbled for his line.
A rampaging Darren Fletcher put United back in the lead in the second half from a Giggs cross, but Bellamy hit back again with a thunderous effort into the top corner from outside the box.
Fletcher headed home again from another Giggs assist with 10 minutes to go and at 3-2 United looked to be cruising.
But England stopper Ferdinand bizarrely chose to try and loft the ball out onto the wing, his attempted pass flopping tamely onto the chest of Welshman Bellamy, who outsprinted Ferdinand to slide the ball beyond Foster.
The board went up for four mintes of injury time, but as five minutes came and went Giggs worked his magic again to leave City manager Mark Hughes to curse the timekeeping, managing a rueful handshake with delighted opposite number Alex Ferguson before joining his players in the tunnel.
United go joint top with 15 points in the English Premier League alongside Chelsea, who play Tottenham in the late kick-off on Sunday.