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 15 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 result leaves United fourth in the table, whilst Albion slip to 12th.
Manchester United ended a run of three consecutive home defeats against Brighton.
1. Manchester United 4-2 Brighton
Manchester United ended a run of three consecutive home defeats against Brighton. Photo: OLI SCARFF/AFP via Getty Images
One of Brighton's better performers. He couldn't have done anything about any of the goals. Many some brilliant saves to keep the score-line down after far too much sloppiness from his teammates. Vital save at 3-2.
2. Bart Verbruggen - 7
One of Brighton's better performers. He couldn't have done anything about any of the goals. Many some brilliant saves to keep the score-line down after far too much sloppiness from his teammates. Vital save at 3-2. Photo: Shaun Botterill/Getty Images
Some promising moments going forward but had a really tough night defensively against Man United's lively forwards.
3. Mats Wieffer - 5
Some promising moments going forward but had a really tough night defensively against Man United's lively forwards. Photo: Zohaib Alam - MUFC/Manchester United via Getty Images
Intriguing battle against Benjamin Sesko, who didn't get on the scoresheet but caused plenty of problems for Van Hecke. Played a lovely pass to Watson who was fouled for the free-kick, which Welbeck brilliantly scored.
4. Jan Paul van Hecke - 6
Intriguing battle against Benjamin Sesko, who didn't get on the scoresheet but caused plenty of problems for Van Hecke. Played a lovely pass to Watson who was fouled for the free-kick, which Welbeck brilliantly scored. Photo: Zohaib Alam - MUFC/Manchester United via Getty Images