Manchester City delivered a dominant performance as an Eric Bailly own goal and a Bernardo Silva strike earned the champions their first Manchester derby victory in five Premier League attempts over their local rivals at Old Trafford.
Pep Guardiola's side went ahead on seven minutes when Bailly diverted Joao Cancelo's cross into his own net.
United briefly rallied when Cristiano Ronaldo's shot was saved by Ederson and Mason Greenwood scuffed the rebound wide.
David De Gea made five big saves in the first half to deny Gabriel Jesus, Kevin De Bruyne, Cancelo, twice, and a Victor Lindelof deflection before City beat the Spaniard's resistance again on the stroke of half-time.
Cancelo set up the second goal when his cross was turned in at the far post by Bernardo, who sneaked in at the far post behind a hesitant Luke Shaw.
The hosts improved in the second half but also lost Shaw to a head injury.
City, who move second with 23 points, almost scored again late on as Phil Foden clipped a post.
A fourth consecutive home match without a win drops United down to sixth with 17 points.
See: Man Utd report | Man City report
Next fixtures
Man Utd: 20 Nov v Watford (A)
Man City: 21 Nov v Everton (H)
Match officials
Referee: Michael Oliver. Assistants: Stuart Burt, Simon Bennett. Fourth official: Robert Jones. VAR: Darren England. Assistant VAR: Dan Robathan.
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