Danny Welbeck returned to haunt Manchester United by scoring his first goal of the season in Brighton's assured 3-1 victory against his old club at Old Trafford.
Roberto De Zerbi's accomplished men move up to third in the Premier League table, three points behind leaders Manchester City, after producing another slick performance in claiming an almost flawless fourth win of the campaign.
Welbeck converted an inviting cross from Simon Adingra on 20 minutes after a delightful dummy by Adam Lallana to enable the incoming former England forward to finish expertly from seven yards.
Pascal Gross added the second with another fine low finish on 53 minutes from Tariq Lamptey's pass before the creative Lamptey picked out substitute João Pedro to rifle a superb third for the visitors on 71 minutes.
United substitute Hannibal Mejbri drilled home a consolation from distance for Erik ten Hag's outclassed side two minutes later.
United thought they had equalised via Rasmus Højlund's finish on 40 minutes, but VAR deemed Marcus Rashford had failed to keep the ball in play from the cutback.
Brighton have won their last four league games against United as they also ended the home season's 31-match unbeaten home run in all competitions.