Chelsea boss Graham Potter suffered a humiliating return to Brighton as his former club ended his unbeaten start with a stunning 4-1 victory at the Amex Stadium on Saturday.
Potter had gone nine games without defeat since leaving Brighton to take charge of the Blues.
But Brighton ruined the Chelsea chief’s first reunion with the Seagulls as their new manager Roberto De Zerbi enjoyed his maiden success following his arrival to replace Potter.
Brighton raced into a commanding half-time lead, with own goals from Ruben Loftus-Cheek and Trevoh Chalobah compounding Potter’s misery following Leandro Trossard’s early opener.
Kai Havertz pulled a goal back just after half-time but Pascal Gross’s late strike rubbed salt into Potter’s wounds.
Potter was jeered when he stepped off the Chelsea team bus and endured mocking, if unrealistic, chants of “you’re getting sacked in the morning” from the Brighton faithful through his side’s dismal display.
It was an afternoon to forget for Potter, whose team dropped to fifth place and now trail leaders Manchester City by eight points.
After securing their place in the Champions League last 16 with a midweek win in Salzburg, Chelsea looked lethargic right from the start of their first defeat against Brighton since 1933.
Chelsea captain Thiago Silva had already twice been forced to head off his own goal-line, first to deny Trossard and then Pervis Estupinan, when Brighton took a fifth minute lead.
Japan winger Kaoru Mitoma claimed the assist on his full Premier League debut, picking out Trossard, who rounded Chelsea keeper Kepa Arrizabalaga to claim his seventh goal of the season.
Albion doubled their advantage with just 14 minutes on the clock.
Solly March’s inswinging corner caused chaos and Chelsea midfielder Loftus-Cheek could only divert the ball into his own net via the underside of the crossbar.
“Potter, what’s the score?” rang around the Amex Stadium as Chelsea’s Christian Pulisic somehow fired wide with the goal gaping after Robert Sanchez pushed away Conor Gallagher’s initial effort.
Spain goalkeeper Sanchez then went one better, producing a stunning one-handed diving save to turn Gallagher’s flicked header over the crossbar.
But Chelsea’s brief revival was extinguished three minutes before the interval.
Chalobah did the damage, diverting the ball beyond Kepa into his own net after Estupinan cut the ball back from the left.
Four minutes after the break, Gallagher delivered an inviting cross from the right following Loftus-Cheek’s lay-off and Havertz escaped Albion’s defence to head home.
Chelsea dominated for much of the final 25 minutes but their embarrassment was complete in the final moments when Gross tapped in on the rebound after Julio Enciso was denied by substitute keeper Edouard Mendy.