Graham Potter suffered a crushing first defeat as Chelsea head coach on his return to former club Brighton and Hove Albion, who claimed a thrilling 4-1 win at the Amex Stadium on Saturday.
Potter was aiming to become the first English boss in Chelsea's history to go unbeaten in his first 10 games, but the Seagulls were ravenous as they earned new coach Roberto De Zerbi his maiden win.
Chelsea's defeat was essentially confirmed by half-time after Leandro Trossard's early strike was added to by own goals from Ruben Loftus-Cheek and Trevoh Chalobah.
Kai Havertz pulled one back just after half-time, but magic was in short supply for Potter and the Blues as Pascal Gross added gloss to the scoreline late on.
De Zerbi's side were straight on the front foot and scored in just the fifth minute.
Kaoru Mitoma's incisive run was followed by an intricate pass into the box for Trossard, who showed exceptional composure to round Kepa Arrizabalaga and slam home.
It was 2-0 soon after, as Loftus-Cheek miscued a clearance from a corner and found his own net.
Moises Caicedo was denied by the post just after the half-hour mark, but Brighton still managed to extend their lead before the break – Chalobah poking Pervis Estupinan's pass beyond Kepa.
Potter withdrew Kepa for Edouard Mendy at the break and Chelsea quickly got themselves a lifeline – Havertz nodding in Conor Gallagher's cross.
The goal was a precursor to prolonged Chelsea pressure, but no comeback followed and Brighton got a fourth in stoppage time, Gross pouncing on the rebound after Julio Enciso tested Mendy's palms.
What does it mean? – Potter's honeymoon period over in resounding fashion
Obviously in terms of form, this result was a shock, but the narrative was already written – Potter losing his first game as Chelsea boss away to Brighton had to happen, didn't it?
The home fans' chants of "you're getting sacked in the morning" probably will not come to fruition, but Potter's side were way off their best. There was very little invention to their play throughout, and in the first half they simply could not cope with Brighton's intensity.
Brighton may have got lucky with the two own goals, but De Zerbi will argue he was due a bit of fortune after a rocky start to life in the Premier League.
Trossard takes the game to Chelsea
Brighton's Belgian forward may not be the biggest, but he certainly knows how to keep a defensive unit on their toes.
He was particularly lively here, having six shots – two more than any other Brighton player – and got four of them on target. One of those, of course, was the first goal, which was brilliantly taken.
Cucurella's unhappy homecoming
Much like Potter, Marc Cucurella was back at Brighton for the first time since moving. It was a day to forget for the Spaniard, who was run ragged by Solly March in the first half. He was unsurprisingly taken off just after the hour.
Key Opta facts
- Brighton secured their first ever league victory over Chelsea at the 15th attempt of trying (D4 L10). Indeed, this was the first time the Seagulls have scored more than one goal in a league match against the Blues.
- Chelsea suffered their first Premier League defeat under Graham Potter (W3 D2 L1), conceding double the number of goals on Saturday (four) as they did in their first five league matches under him.
- Leandro Trossard became the first player to score a club's first five Premier League goals under a specific manager (under Roberto De Zerbi). Indeed, the Belgium international has scored 25 Premier League goals, with only Glenn Murray and Neal Maupay (26 each) netting more for the Seagulls in the competition.
- Chelsea scored two own goals in a single Premier League game for the first time, becoming the first side to put through their own net twice in the opening 45 minutes since Everton against Southampton in April 2014.
Chelsea are at home to Dinamo Zagreb in the Champions League on Wednesday and then host Arsenal four days later. Brighton go to Wolves next Saturday.