Brighton hammer Graham Potter's Chelsea on his return to Falmer Stadium
Manager Graham Potter's unbeaten start at Chelsea was abruptly ended as his former club Brighton thrashed his charges 4-1 in the Premier League on Saturday.
Rampant Albion 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 the restart but the Blues were unable to prevent a first defeat in 10 games since the sacking of Thomas Tuchel as Pascal Gross rubbed salt into the wound in added time.
The remarkable result at a raucous Amex Stadium was the Seagulls' maiden victory under new head coach Roberto De Zerbi and a first over the west London club since 1933, with the unforgiving home supporters gleefully revelling in their ex-manager's suffering.
Potter returned to Sussex with six wins and three draws from his nine fixtures at Stamford Bridge and looking to inflict further punishment on an Albion side who began the day with just two points from a possible 15 since his departure seven weeks ago.
He received jeers - and a smattering of applause - when he stepped off the team coach, while there were further boos when he emerged from the tunnel.
Brighton fed off their fans' hostile energy and quickly took control of the contest during a blistering start.
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 three sides of the ground erupted in the fifth minute.
Japan winger Kaoru Mitoma claimed the assist on his full Premier League debut, delightfully dancing into the box and offloading to in-form Trossard, who rounded goalkeeper Kepa Arrizabalaga before emphatically dispatching his seventh goal of the season beyond former Seagulls defender Marc Cucurella.
Potter was soon looking stunned in the away dugout as Albion duly doubled their advantage with just 14 minutes on the clock.
Solly March's inswinging corner from the right caused chaos in the Blues box and recalled midfielder Loftus-Cheek could only divert the ball into his own net via the underside of the crossbar.
The quick-fire goals produced a deafening noise inside the ground, with chants of "Potter, what's the score?" growing louder and followed by playful questioning of his job security.
Despite their dreadful start, Chelsea were far from dejected and had numerous chances to halve the deficit as the breathless, end-to-end action continued.
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.
Havertz was also kept out, while Raheem Sterling was later denied a penalty when he went down under a challenge from Gross.
Any growing momentum for the visitors was extinguished three minutes before the break as Chelsea again contributed to their own downfall.
This time the sliding Chalobah did the damage, diverting the ball beyond Kepa after rampaging full-back Estupinan cut the ball back from the left.
Potter replaced keeper Kepa with Edouard Mendy for the second period due to an apparent injury but quickly had reason for greater optimism.
Midfielder Gallagher delivered an inviting cross from the right following Loftus-Cheek's lay-off and Havertz escaped Albion's defence to head home unmarked.
Sanchez prevented a Gross own goal as the Blues pushed for another, before Potter hooked the ineffectual Sterling and Brighton's player of the season for 2021-22 Cucurella, with Ben Chilwell and Pierre-Emerick Aubameyang introduced.
Chelsea dominated for much of the final 25 minutes but could not make further inroads on the scoreboard and were eventually sent home embarrassed after Gross tapped in on the rebound after lively substitute Julio Enciso was denied by Mendy.
Italian De Zerbi jubilantly celebrated a milestone moment with his new fans on a chastening afternoon for predecessor Potter.