Brighton gained sweet revenge on Thursday for their defeat by Manchester United in the FA Cup semi-finals, with Alexis Mac Allister converting a 99th-minute penalty to dent the visitors' Champions League hopes.
Classy Brighton dominated possession but lacked a cutting edge until Luke Shaw's handball deep into stoppage time presented them with an opportunity to take all three points.
The 1-0 win completes a league double for the Seagulls against United, who beat Erik ten Hag's men in their first match of the season but suffered a painful defeat on penalties in last month's FA Cup semi-final at Wembley.
United remain in the fourth and final Champions League qualification spot in the Premier League, four points ahead of fifth-placed Liverpool with a game in hand, while Brighton are up to sixth. "There is a God of football," Brighton boss Roberto De Zerbi told Sky Sports. "We deserved to win the semi-final but lost on penalties but today we won with a penalty.