Despite a positive start to proceedings, the Reds were behind on 20 minutes when former United man Danny Welbeck tapped home from close range. Rasmus Hojlund thought he may have got his first goal for the club but VAR adjudged the ball had gone out of play in the build-up.
The Seagulls pressed on after the first-half scare and made it 2-0 through Pascal Gross. Joao Pedro added a third with 20 minutes remaining to put the match beyond doubt but Hannibal Mejbri bagged a consolation with his first for the senior team moments later.
After a disappointing afternoon at the Theatre of Dreams, MEN Sport has taken a look at things you may have missed this weekend.
Luck hasn&apost been on United&aposs side this season when it comes to injuries but the knocks picked up by likes of Mason Mount and Kobbie Mainoo have allowed Dan Gore the chance to soak up the experience of being a regular in the matchday squads. The youngster was named on the bench against Brighton and has now been included in all three of United&aposs last three matchday squads.
The 18-year-old is yet to make his senior debut for United but Ten Hag clearly likes the look of him. Mainoo looks set to have a bright future at United having been included in a whole host of matchday squads last season and Gore could be next in line.
The Reds suffered their first home Premier League defeat of the season yesterday and it was also the first time they had been beaten in a league game at Old Trafford for over a year. The last team to beat them? Brighton.
United&aposs loss to the Seagulls last year when Graham Potter was in charge came just before the heavy defeat at Brentford. Hopefully the Reds avoid a similar fate on Wednesday night in Munich.
Once Welbeck was announced as starting for the visitors, it seemed almost inevitable he would have a say in the result. It has started to feel as though the 32-year-old always gets a goal against his old club and the truth is not far off.
Incredibly, Welbeck has scored against Ten Hag, Ole Gunnar Solskjaer, Jose Mourinho and Louis van Gaal&aposs United teams. United may hope he isn&apost available for the reverse fixture on the last day of the campaign.