Manchester United secured a first league double over Manchester City since the Sir Alex Ferguson era with a 2-0 win at Old Trafford.
Anthony Martial struck on the half hour, squeezing a volley under visiting goalkeeper Ederson, before United sat deep and defended resiliently.
Sergio Aguero had a goal ruled out for offside and David De Gea made a couple of smart stops, but City struggled to convert their possession into clear chances.
City made a double substitution bringing on Riyad Mahrez and Gabriel Jesus in the 59th minute, which gave them more pace up front but it was perhaps too little too late as United dug their heels in.
Scott McTominay pounced on an awful Edersen throw in injury time to seal the three points, fizzing a shot into the empty net from 35 yards as United moved to within three points of fourth-placed Chelsea.
The result, which leaves Liverpool two wins from a maiden Premier League title, saw United defeat their neighbours home and away for the first time since the 2009-10 campaign.
City next face Arsenal at home on Wednesday, while United are in action in the Europa League last 16 against LASK on Thursday.