Following a miss by Solly March, Erik ten Hag’s squad triumphed 7-6 in penalty kicks, keeping them on track for a domestic cup double.
The semi-final in front of over 81,000 spectators ended 0-0 after extra time, with neither team displaying the cutting edge required to break the deadlock.
As a result, in the first-ever meeting between the rivals in an FA Cup final, Man United will have the opportunity to derail Man City’s effort to duplicate their remarkable achievement of winning the treble of Champions League, Premier League, and FA Cup.
However, the Red Devils, who won the League Cup earlier this season to snap a six-year trophy drought, will need to improve their form if they are to compete with Pep Guardiola’s hot team.
While speaking about their Europa League horror show against Sevilla, Ten Hag told the BBC, “On Thursday I saw a team I didn’t recognise but today we went back to usual.
“I could see determination and resilience. We fought for every yard and competed in every battle. We had good chances.”
Following Thursday’s 3-0 defeat in Spain, which meant a 5-2 defeat on aggregate in the Europa League quarter-finals, Luke Shaw came in at centre-back for the suspended Harry Maguire, with Marcus Rashford and Bruno Fernandes replacing Jadon Sancho and Marcel Sabitzer.
Brighton, who lost the FA Cup final replay to United 40 years ago, had won the previous two league meetings and arrived at Wembley on a high after defeating Chelsea last week.
The south-coast club took the lead first, with Kaoru Mitoma taken down awkwardly on the edge of the box by Antony in the sixth minute.
Alexis MacAllister of Argentina scored a magnificent curling effort that David De Gea did well to keep out before Julio Enciso flashed a shot wide.