It was the nerveless Alexis Mac Allister who blasted home the decisive spot kick deep in injury time to claim a memorable win and keep their European hopes on track.
Albion were out to avenge their FA Cup semi-final loss to the Red Devils at Wembley Stadium just two weeks ago.
The game remained goalless following a lively opening 45 minutes in which Antony fired wastefully wide after Bruno Fernandes’ pass carved open Albion’s defence inside two minutes, before Kaoru Mitoma intercepted an under-hit Victor Lindelof pass and raced clear at the other end only to thump his effort into the head of David De Gea with Julio Enciso awaiting a tap-in.
United goalkeeper De Gea was visibly shaken by the unconventional stop but was deemed fit to continue after receiving treatment.
Casemiro later headed narrowly over for Ten Hag’s side, while Brighton keeper Jason Steele produced smart saves to deny low efforts from Marcus Rashford and Martial.
After the break Brighton had their chances, most notably when Danny Welbeck sidefooted over from Mitoma’s pass, and Steele once again produced a fine stop to thwart Fernandes.
Mitoma also felt aggrieved when he was bundled over in the box by Wan-Bissaka, referee Andre Marriner waved it away and there was no further action following a brief VAR check. Chants of ‘the Premier League is corrupt’ bellowed around the stadium.
Solly March, the man who missed the penalty in the semi-final shootout, was excellent from the bench and fired a couple of efforts close, while Mac Allister forced a late low save from De Gea down sharply to his right.
Albion pushed to the end and snatched the lead deep into added time when Mac Allister converted from the penalty spot after Luke Shaw was penalised for handball following VAR intervention.
Another cracking and high quality match...Here’s how the Albion players rated...
9. Kaoru Mitoma 7
Had a great chance to score after five minutes. He was clean through and his powerful shot smacked De Gea square in the face. Always a danger down the left flank at times his final ball let him down Photo: Ryan Pierse
10. Facundo Buonanotte 7
Composed on the ball and always seems to pick the right pass. Curled a left footed effort just beyond the post on the stroke of half time. Faded after the break and replacedby March Photo: Mike Hewitt
11. Billy Gilmour 8
Quick to the press and good use of the ball. Stuck to his task and remained disciplined. Gaining De Zerbi's trust all the time. Photo: Matthew Peters
12. Danny Welbeck 7
Fired a good chance over the bar on 58 minutes. Huge amount of work rate but just lacked that killer touch at the vital moment. Photo: Matthew Peters