Manager Pep Guardiola says Manchester City must improve for the Champions League final after Brighton came back to beat his 10-man side at Amex Stadium.
New Premier League champions City, who face Chelsea in the European showpiece on 29 May, blew a two-goal advantage to lose 3-2 on a raucous evening on England's south coast, played out in front of 7,495 fans.
Ilkay Gundogan silenced the supporters with a second-minute opener, but City were a man down after nine minutes, when Joao Cancelo was judged to have brought down Danny Welbeck, who was goal side of the defender.
Phil Foden's superb solo effort put the visitors 2-0 up - but Leandro Trossard gave Brighton hope with a cool close-range finish, and the home side then put intense pressure on the champions' goal.
Adam Webster levelled, rising highest in the box to head home Pascal Gross's delivery and then, with 14 minutes left, Dan Burn sent the fans into raptures with the winner, following up his own blocked shot to steer the rebound into the corner of the net