Graham Potter saw his return to Amex Stadium end in humiliation for his side as Brighton trashed Chelsea to claim their first victory under new manager Roberto de Zerbi.
The victory was the first loss for Potter in 10 games in all competitions since he became the Blues gaffer.
Brighton via Leandro Trossard took the lead in a dramatic fashion after Thiago Silva lost possession in his own half to give away a cheap opener for the Seagulls.
Then Ruben Loftus-Cheek and Trevor Chalobah made worse Chelsea’s fate as they bundled the ball on different occasions into their own net to extended Brighton’s lead before the break.
Kai Havertz headed home Conor Gallagher’s deft cross two minutes after the break to keep hopes alive for the visitors with all efforts afterwards impotent to giving them a comeback.
Pascal Gross scored a close-range goal to kill off the game and a miserable afternoon for the Blues.
The victory takes Brighton to seventh, while Chelsea stay fifth.