Robin van Persie scored an injury-time free-kick winner to make it 3-2 and end City’s 37-game unbeaten home league run stretching back two years.
United boss Fergie said: “We’ve done it in the past against City but today was a special one simply because they haven’t lost at home for two years and both teams are contending at the top of the league.
“It was a fantastic game — you couldn’t take your eyes off it.
“Intensity, passion, competitiveness, everything was there, it was really fantastic. We played very well and deserved to win overall.”