Brajan Gruda opened the scoring at Old Trafford with an emphatic finish on 12 minutes before Danny Welbeck fired home an even more stunning strike with 65 minutes of the match played.

Benjamin Sesko pulled a goal back late on but the Seagulls deservedly saw out the tie to secure their place in the fourth round.

Darren Fletcher took charge for just the second time following the exit of Rubin Amorim, after a 2-2 Premier League draw with Burnley that they should have won.

And it was the home team who started the brighter of the two sides, with Diogo Dalot forcing a strong save from an advancing Jason Steele in the Brighton goal.

Dalot was free again just moments later but this time he blasted his shot over the target.

A seventh minute Fernandes free-kick then needed tipping around a post by Steele as Kobbie Mainoo directed the ball goalward.

But Gruda needed only one chance when he slammed home from close range after pouncing on Lisandro Martinez's goal line clearance. Georginio Rutter had headed a Welbeck cross on target that Martinez did well to get anything on.

Benjamin Sesko should have done better on 16 minutes after a well-time run to pick up a pass from Martinez, but his lob lacked any real power to beat Steele.

Both sides were somewhat guilty of wasting half chances for the rest of the first half, with Cunha the main culprit for United as Steele kept his goal intact.

The second period, meanwhile, began with United momentarily on top before Brighton began to open up their defence.

A 54th minute Gruda free-kick was pelted over the bar by Joel Veltman before the same player fired in a shot that was blocked en route to goal.

Joshua Zirkzee and Shea Lacey were brought on to replace Mainoo and Mason Mount as Fletcher looked for a way back into the tie.

But it just two minutes later when the Seagulls doubled their lead through an unstoppable shot from Wellbeck that left Senne Lammens with no chance.

The former Man Utd striker was played in on the edge of the area by Gruda and took the ball away from Leny Yoro with a good first touch before blasting in the top left corner of the net.

With time running out, United introduced Harry Maguire and Casemiro to replace Martinez and Manuel Ugarte, to little effect.

Sesko tried his luck with a shot on the volley on the edge of the area that was too close to Steele during a better spell of possession for the home side, before Lacey saw a curling shot hit the roof of the net.

A goal was certainly expected by United fans and they were ultimately rewarded when Sesko headed home a deep inswinging corner to give them hope heading into the last five minutes.

A moment of madness from young Lacey saw him dismissed for a second yellow card, as he threw the ball down in anger after a loss of possession, while the dying minutes saw Brighton use every trick in the book to wind down the clock.

Manchester United dumped out of the FA Cup in the third round by Brighton