It means the two Manchester rivals will face off for the first time in the final of an FA Cup on June 3, giving Man United the chance to possibly stop Man City completing the treble -- a feat achieved only once before in England, by Man United in 1999.
1. Mental toughness carries Man United to FA Cup final against Man City
United manager Erik ten Hag said he wanted a response to his side's dismal Europa League exit to Sevilla on Thursday and, at least in terms of character, he got it. There were periods of Sunday's game when United were second best to Brighton, but when it became a mental test in the shootout, they held the edge.
Man United had lost seven of their previous eight penalty shootouts, including in the 2021 Europa League final against Villarreal, but they got the better of Brighton to ensure a first all-Manchester FA Cup final against Manchester City in June.
Victor Lindelof scored the deciding penalty after March had missed for Brighton -- but there should be special mention for Jadon Sancho and Marcus Rashford, who both stepped up to convert from the spot nearly two years after they missed in England's defeat to Italy in the European Championship final. Sancho has had a miserable season and was poor against Sevilla on Thursday, but he showed great strength to first volunteer for a penalty and then tuck it away.
There was a danger the season could unravel after their disaster in Spain, but Ten Hag's team have got a lot of play for in the next six weeks with an FA Cup final to look forward to and a place in the top four up for grabs.
2. Brighton's midfield outplayed Man United's
Midfield is one of many areas of the United squad which needs to be strengthened, and Ten Hag could do worse than look at Brighton pair Alexis Mac Allister and Moises Caicedo, who made Brighton the better team for stretches.
The pair of players are so important to the way Brighton manager Roberto De Zerbi wants his squad to play, and both got special attention from Man United midfielders Christian Eriksen and Bruno Fernandes when Brighton were trying to play out from the back. But centre-backs Lewis Dunk and Adam Webster trusted the ability of Mac Allister and Caicedo to find half a yard of space and flick the ball off to another blue shirt.
Time and time again United tried to force Brighton into mistakes, but more often than not, Mac Allister and Caicedo guided them through the pressure. Pep Guardiola hailed Brighton's build-up football as "the best in the world" recently, and at Wembley they lived up to the billing.
In contrast, United often looked to go long to Anthony Martial and there was a reason why, after 25 minutes, Brighton had completed double the number of passes. Brighton had the better chances in 90 minutes and looked the most likely to score until the shootout -- but Brighton, and in particular Mac Allister and Caicedo, can be proud of their performance.
3. Brighton's growth under De Zerbi has been remarkable
This was only Brighton's second FA Cup semifinal since reaching the final in 1983 -- when they lost in a replay to United -- but days like this will become the norm if they keep progressing in the same way under De Zerbi.
The Seagulls will never have the budget to compete regularly with the likes of Man United, Manchester City, Chelsea and Arsenal at the top of the Premier League -- but with the Italian manager in charge, it's realistic to believe they can keep challenging for a place in Europe. Given the upheaval caused by losing Graham Potter to Chelsea in September, it's remarkable what De Zerbi has been able to achieve despite being parachuted into the job mid-season.
The problem for Brighton is that their best players will always attract attention from top clubs -- evidenced by Arsenal's pursuit of Caicedo in January -- and it's nearly impossible to keep them all. Losing key personnel summer after summer puts pressure on the recruitment department to keep unearthing hidden gems but the development of players like March has already shown that De Zerbi is a coach who can get the best out of a squad.
The Brighton fans enjoyed their day out at Wembley, turning their end into a sea of blue and white flags before kickoff. They will be back soon.
Best and worst performers
Best: Moises Caicedo, MF, Brighton
United's two No. 8s tried to put him under pressure, but he was still good enough to bounce the ball around in tight spaces.
Best: David De Gea, GK, Man United
He had a shocker against Sevilla but made three good saves here, the first from Mac Allister's free-kick after just seven minutes.
Best: Victor Lindelof, DF, Man United
Defended well in place of Lisandro Martinez and Raphael Varane and scored the decisive penalty in the shootout.
Worst: Christian Eriksen, MF, Man United
Only just back from a serious injury, but he looked short of energy and was substituted early in the second half.
Worst: Julio Enciso, FW, Brighton
The 19-year-old forced David De Gea into a good save but he was sometimes a little naive with his use of the ball.
Worst: Antony, FW, Man United
The Brazilian winger got into some good positions, but his decision-making around the Brighton box infuriated Ten Hag.
Highlights and notable moments
VICTOR LINDELOF SENDS MAN UNITED TO THE FA CUP FINAL 😱🏆 pic.twitter.com/8KGIREVTb6— ESPN FC (@ESPNFC) April 23, 2023
After the match: What the managers and players said
Manchester United manager Erik ten Hag on his team's response after the Sevilla loss: "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."
Ten Hag on goalkeeper David de Gea's performance: "I was very impressed with him. He made some brilliant saves. It hurt when he made mistakes on Thursday."
Key stats (provided by ESPN Stats & Information research)
Man United advance to 21st FA Cup final to tie Arsenal for most all time.
Man United have reached the final of both major domestic cup competitions in a season for the third time, previously doing so in 1982-83 and 1993-94. They defeated Newcastle in the Carabao Cup final.
Man United have made the final of both FA and League Cup for first time since 1993-94 (won FA, lost League cup).
Brighton have never won a competitive match at Wembley Stadium, drawing one and losing four of their five visits. This run started against Manchester United in the 1983 FA Cup final, drawing 2-2 and then losing 4-0 in a replay.
Man United were been shut out in regulation in consecutive games this season for the first time (all competitions).
Brighton & Hove Albion: The Seagulls resume their Premier League campaign with a visit to Nottingham Forest on Wednesday at 2:30 p.m. ET.
Manchester United: The fourth-place Red Devils head to Tottenham to face fifth-place Spurs in the Premier League on Thursday at 3:15 p.m. ET in a match that could have major top-four implications for Champions League. The FA Cup final between Man United and Man City is set for June 3 at Wembley.