Manchester City took control of the Premier League title race with two games remaining after a derby victory saw them leapfrog rivals Manchester United at the top of the table.
Vincent Kompany's header in first-half stoppage time gave City the win that means they have wiped out the eight-point advantage held by United three weeks ago, and move to the summit on goal difference.
City needed the victory while Sir Alex Ferguson knew a draw would suit his purposes more than opposite number Roberto Mancini - and this was reflected in his team selection that saw Wayne Rooney desperately isolated as a lone striker.
In a game of few chances, City were the more positive side and deserved the three points on offer in what had been labelled the biggest game in the Premier League's 20-year history.
United, in contrast, were passive, poor and lacking inspiration despite the high stakes, failing to get a shot on target as City keeper Joe Hart enjoyed a virtually untroubled night.
And Ferguson's frustrations boiled over in the closing stages when he angrily confronted Mancini after City substitute Nigel de Jong was booked for fouling Danny Welbeck.
The Italian delighted City's support by giving the Scot as good as he got - complete with gestures - as they went head-to-head before fourth official Mike Jones stepped in to restore order.
With United dropping eight points out of their last 12, the momentum and advantage is now with City. Mancini knows victory in their last two games, away at Newcastle United and at home to Queen's Park Rangers, would give them their first title since 1967-68.
City's recent resurgence has also proved decisive for their goal difference as they now hold an eight-goal advantage over United and, as referee Andre Marriner sounded the final whistle, their fans joyously celebrated a victory they clearly felt would prove decisive.