Alexis Mac Allister fired Brighton to sixth in the Premier League by converting a dramatic added-time penalty to dent Manchester United's Champions League hopes.
The Argentina World Cup winner emphatically dispatched the ball into the top left corner nine minutes beyond the regulatory 90 after Luke Shaw was penalised for handball following VAR intervention.
Albion's 1-0 win from a pulsating Amex Stadium contest moves them above Tottenham and Aston Villa, while leaving United looking over their shoulders at fifth-placed Liverpool.
The Seagulls sit just four points behind Jurgen Klopp's Reds with two games in hand thanks to the stunning late twist and are are now eight points behind fourth-placed United with a game in hand.
Goalkeeper Jason Steele told Sky Sports: "That was special. It was a big night for us and obviously you can't beat a last-minute winner.
"It wasn't about revenge (after losing to United in the FA Cup semi-final). Did we have a little bit of extra motivation? Probably. But I don't think it spilled over and we deserved to win the game."
Seagulls boss Robeto De Zerbi felt justice had been served after Brighton avenged their recent FA Cup defeat to United.
"There is a god of football because we deserved to win in the semi-final and we lost on penalties," De Zerbi told Sky Sports.
"But in both games I think we played better than United. The last result was unfair.
"We dominated the game against one incredible team, but we have to play another six very tough games.
"Monday we play the first game against Everton and we have to win, because if we don't we lose these three points."
Shaw owned up to his stoppage-time mistake that cost United a point.
"It hurts a lot. I got a little nudge but of course the hand shouldn't be there," Shaw told Sky Sports.
"Of course I own up to it and take it on the chin. It cost us the game and it's tough.
"The free-kick before the corner was never a foul. I'm not looking for excuses for what I've done, but there's no way that should have been given a foul and that corner shouldn't have happened.
"I can't change that, but hands up. It's a silly mistake that cost us a point at the end."
