Managerless Manchester United completed an unwanted cup double as former striker Danny Welbeck helped Brighton send them crashing out of the FA Cup at Old Trafford.

In front of his old boss Sir Alex Ferguson and with former team-mate Darren Fletcher in interim charge at his old club, Welbeck belted home Brighton's second to send them into the fourth round.

It was the 35-year-old's eighth goal against United and his sixth visiting the stadium he used to call home.

The thunderous drive into the roof of Senne Lammens' goal doubled a lead given to Brighton by Brajan Gruda's first-half opener.

Benjamin Sesko's header five minutes from time breathed life into the home side but 18-year-old home substitute Shea Lacey was sent off in the final minute and Brighton held on for their first ever FA Cup victory against the 13-time winners at the seventh attempt.

For United, this defeat followed up the embarrassing EFL Cup second-round exit at League Two Grimsby, meaning they had exited both domestic cup competitions at the earliest possible stage for the first time since 1981-82.

It also means Fletcher's two-game stint as interim boss contributed a disappointing Premier League draw against Burnley and this home defeat to a campaign that is beginning to unravel.

United have now won once in their last seven games, with title contenders Manchester City and Arsenal their next two opponents.

Within the next 48 hours, the club are due to name who will replace Ruben Amorim until the end of the season, with Ole Gunnar Solskjaer and Michael Carrick viewed as the frontrunners.

Man Utd analysis: Season on the brink of collapse

Over the past five weeks, a season that has been delicately placed for weeks has now suddenly lurched downwards to the point where United are staring into the abyss.

While seventh in the Premier League is not catastrophic, if results against Manchester City and Arsenal go to form, they could be firmly in the bottom half of the table by the time they entertain Fulham on 1 February, where the 1958 Group of supporters plan a mass demonstration against the ownership.

The backdrop could hardly be worse for any new manager and does not offer the same immediate uplift opportunity Solskjaer enjoyed when he replaced Jose Mourinho in 2018.

It also means United face a 40-game season, their lowest since before the First World War. This is hardly going to help the financial situation Sir Jim Ratcliffe has pledged to improve, but has now added to substantially twice by sacking managers he backed at the end of the previous season - and to the tune of more than £200m.

There was not even consolation today in the form of youth.

Teenage forward Lacey is predicted to hit the heights in his career. However, he will not remember his Old Trafford debut fondly.

Already booked after being introduced as a substitute with half an hour remaining, Lacey reacted to a decision going against him by bouncing the ball down in disgust and the dismissal left him almost in tears as he left the field.

Brighton analysis: Seagulls finally end Man Utd cup curse

Brighton fans will feel they owed Manchester United one when it came to the FA Cup.

They might have won on their last three trips to Old Trafford prior to this season, but in this competition, they had nothing but painful memories.

The biggest was that 1983 'Smith must score' FA Cup final, when Seagulls striker Gordon Smith's shot in the last minute at Wembley was saved by Gary Bailey, thus denying them victory, with defeat following in the replay.

Three seasons ago, the two sides met at Wembley again. Most observers felt Brighton were clearly the better side in the semi-final, but it was United who prevailed, on penalties.

This time Fabian Hurzeler's side got the win they deserved.

Aside from the opening couple of minutes, when goalkeeper Jason Steele denied Diogo Dalot and Bruno

Fernandes, Brighton looked the more dangerous.

The 12th-minute opener came after Georginio Rutter's shot from Welbeck's cross was booted off the line by Patrick Dorgu and Gruda pounced on the rebound.

Welbeck claimed the crucial second goal as, while Sesko's late header lifted the home fans, Brighton's players kept calm to confirm a third-round exit for United for only the third time in 41 FA Cup ties.

What's next for these teams?

Manchester United entertain local rivals Manchester City in the Premier League at Old Trafford on Saturday, 17 January (12:30 GMT), while Brighton play Bournemouth at the American Express Stadium on Monday, 19 January (20:00 GMT)

(BBC)