Albion almost staged an incredible comeback from three goals down but Bryan Mbeumo’s second of the night – in the sixth minute of injury-time – made sure of the victory.
The hosts were in charge for 73 minutes, with goals from Matheus Cunha, Casemiro and Mbeumo giving Ruben Amorim’s team a three-goal lead.
But Welbeck’s customary goal against his former team – a classy free-kick – gave the Seagulls hope, with 16 minutes of normal time remaining.
With seven minutes added on, you knew there was time for two more goals. Albion got one of those – with substitute Charalampos Kostoulas scoring his first in Brighton colours.
The Greek striker nodded in at the near post from James Milner’s corner – setting up a grandstand finish.
But Mbeumo extinguished any hopes of a sensational comeback with a powerful strike into the roof of the net. It was virtually the last kick of the game.
The match was not without its controversies. There was a big first-half penalty appeal, before the opening goal, when Amad went down under a challenge from Maxim De Cuyper. Play was allowed to continue and it did not impact the hosts’ momentum.
Fabian Hurzeler will no doubt be furious with two controversial decisions against his team, though. Rutter was adamant he was fouled by Luke Shaw in the build-up the third United goal.
And then, referee Anthony Taylor decided not to send Patrick Dorgu off, after he brought down Minteh on the edge of the box – as the Brighton man looked to be through on goal. Albion scored free-kick, anyway, but Hurzeler will argue they should have been up against ten men for the remaining 23 minutes.
The result leaves United fourth in the table, whilst Albion slip to 12th.
5. Lewis Dunk - 6
Sloppy at times but also showed great composure, in moments, to take the pressure of his teammates. Mbeumo's first goal went through the Brighton skipper's legs, leaving Verbruggen no chance. Photo: Ash Donelon/Manchester United via Getty Images
6. Maxim De Cuyper - 5
First start since the trip to Bournemouth on September 13. He was subbed off injured after just 24 minutes that day. He's been effective off the bench in recent weeks but really struggled today. Amad gave him a torrid time. Very fortunate not to give a penalty away after a touch-and-go moment with the Ivorian winger. Replaced by Tommy Watson after 59 minutes. Photo: Zohaib Alam - MUFC/Manchester United via Getty Images
7. Yasin Ayari - 5
Hooked on the hour mark after a really sloppy performance. It was uncharacteristic from the Swedish international, who is one of Hurzeler's key men. Photo: Ash Donelon/Manchester United via Getty Images
8. Carlos Baleba - 5
If this was an audition ahead of a potential move to Old Trafford, it didn't go to plan for Baleba. He was outperformed by Casemiro in the middle of the park. Booked for foul on compatriot Mbeumo. Some nice moments but not enough to make a telling impact. Replaced after 59 minutes. Photo: OLI SCARFF/AFP via Getty Images