Balotelli's heroics helped Roberto Mancini's side end United's 18-month, 37-game unbeaten run at Old Trafford and lifted table-topping City five points clear of the reigning Premier League champions. Sergio Aguero was also on the mark for City as United played for almost the entire second half with only 10 men after the dimissal of defender Jonny Evans, who had been badly at fault for the first goal.
And there were two late goals for substitute Edin Dzeko, with David Silva also scoring, as United leaked three goals in as many minutes in stoppage time. It was an extraordinary afternoon in the history of both clubs, with City recording their biggest win at Old Trafford since a 6-1 victory here in January 1926 and United suffering their heaviest ever Premier League defeat. It also marked a remarkable turn of events for Balotelli who had made the headlines after the fire brigade was called to his Cheshire home in the early hours of Saturday to put out a blaze started by igniting fireworks in his bathroom.
Almost inevitably, the opening goal came from Balotelli after City had weathered a strong opening from the hosts. Evans gave the ball away needlessly in the 21st minute and allowed City to launch a devastating counter-attack. Silva slipped a pass into the inside-left channel for James Milner, who pulled the ball back for Balotelli with Evans failing to mark his man closely enough. The Italian produced a fine low shot from 18 yards which flew into the bottom right-hand corner of the United goal beyond the dive of David de Gea.
Not satisfied with that, Balotelli, without a smile on his face, then lifted his jersey to unveil a t-shirt bearing the message "Why Always Me?". It seemed a fitting question, given events of the weekend, but the 21-year-old's footballing abilities remain unquestioned whatever his problems away from the game, even if his t-shirt slogan earned him a yellow card. Matters did not improve for United after the interval. A minute after the restart, Silva's neat through ball found Evans the wrong side of Balotelli and the Northern Ireland defender blatantly pulled back his man.
Referee Mark Clattenburg had no choice but to show Evans a straight red card. Reduced to 10 men, United might have gone further behind when Micah Richards powered towards goal, following an Aguero mishit, and shot wildly over. Young did better when he robbed Milner in the 57th minute and bore down on goal, Richards' last-ditch block preventing a shot. But that was a rare glimmer of optimism for United fans and, on the hour, City had wrapped up the points with another beautifully-worked goal.
Milner and Silva exchanged passes, the latter back-heeling to the former who reached the by-line before drilling the ball across goal to the far post where Balotelli converted his second of the afternoon. City added a third on 68 minutes through Aguero. Milner's pass freed Richards down the right and he pulled back the perfect cross into the six-yard area where Aguero comfortably converted from close range. Fletcher claimed United's consolation, nine minutes from time, when he swapped passes with Javier Hernandez and curled a perfect finish into the top-right corner of the City goal from 20 yards.
But United would not be spared complete humiliation and, in the 90th minute, Gareth Barry flicked on a corner to the far post where Joleon Lescott crossed for Dzeko to knee into the net from close-range. A minute later, Silva was played clear by Dzeko and sprinted half the length of the field before coolly placing the ball past de Gea. And, in injury-time, Dzeko was again on the mark, another counter-attack sprung by a slide-rule Silva pass which allowed the forward to advance and beat the exposed de Gea yet again.