Bruno Fernandes and Luke Shaw struck early in each half as Manchester United ended Manchester City's 21-match winning run with a stunning 2-0 derby victory.
Fernandes scored a penalty after just two minutes at the Etihad Stadium and Shaw added the second on 50 minutes as United inflicted a first defeat on their rivals since November.
The result cut City's lead over United at the top of the Premier League to 11 points and, while it may be a stretch to suggest the title race has been reignited, it has slowed what was looking like a procession.
It may certainly rejuvenate United, who might have feared being dragged into a battle for a top-four place after an indifferent series of performances.
The only downside for the visitors was the loss of Marcus Rashford through injury in the second half.