Following a tense 120 minutes in which neither team could break the deadlock, Solly March skied his penalty to present Victor Lindelof with the opportunity to take the Red Devils to their second domestic final of the season, which he took.
March was the only player to miss out of the fourteen spot-kick takers, in what was near-perfect demonstration of how to take penalties under pressure.
United will now face Manchester City in the final on June 3, while Brighton will now have nine league games to try and cement a place in a European competition next season.
The result means the Red Devils can put Thursday’s disappointing exit from the Europa League behind them and look forward to a potential second trophy entering the cabinet at the end of the season.
Despite having less of the ball in the first half, United had the best chances, in what was an intriguing game throughout. Fernandes saw one effort well-saved and another pulled just wide of the post.
Brighton built up well from the back with a number of slick passing moves, but lacked a killer final pass. Alexis Mac Allister had a free-kick tipped round the post by De Gea, in what was Albion best chance in the early exchanges.
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The second half was just as edgy as the first, with few clear cut chances for either side. Enciso had a half volley tipped over the bar by De Gea from 12 yards out, with the resulting corner seeing Welbeck head wide at the back post unmarked, when he should have scored.
In extra time, Robert Sanchez brilliantly stopped Rashford’s curling effort to keep the game at 0-0, while a heavy touch let Karou Mitoma down as he was bearing down on David De Gea’s goal, as penalties loomed ever closer.
Having already lost one shootout this season to Charlton in the EFL Cup, in which March also missed by firing his penalty over the bar, Brighton managed to score all their first six penalties with ease.
Having gone 5-4 ahead, Sanchez will have been disappointed not to have saved Sabritzer’s deciding kick, as he watched the ball squirm through his hands and into the net.
But March’s miss means Brighton’s wait for a second FA Cup final appearance continues though, here are the Brighton player ratings from today’s game.
1. Robert Sanchez - 7/10
Was largely untested until extra time and then made an outstanding save to deny Rashford. Will be disappointed not to have saved Sabitzer's penalty. Photo: Alex Davidson
2. Pascal Gross - 6/10
Dealt with the threat of Rashford well and managed to link up nicely with March on a number of occasions. Deserved at least one assist from one of the delicious corners he whipped in. Excellent penalty in the shootout. Photo: Clive Rose
3. Lewis Dunk - 7/10
Played out from the back well with Webster, including some lovely looking line-breaking passes. Received little threat from a passive Martial. Ice in the veins to take and score the fifth penalty. Photo: Matthew Peters
4. Adam Webster - 7/10
Played a number of nice passes to kickstart attacking moves for Brighton and made some timely and much-needed blocks and tackles to prevent United from scoring. Calmly dispatched his penalty. Photo: Mike Hewitt