Pep Guardiola fell to a fourth successive defeat for the first time in his managerial career as Brighton came from behind to beat his Manchester City side.
It is the first time since 2006 that City have lost four in a row.
The Premier League champions looked on course to end their disappointing sequence when Erling Haaland capped an impressive opening at Amex Stadium in the 23rd minute, scoring at the second attempt from Mateo Kovacic’s pass.
Brighton, however, held their nerve, taking complete control after the break – and it was only their poor finishing that prevented them drawing level before substitute Joao Pedro pounced in a scramble 12 minutes from time.
City, who had looked increasingly vulnerable, were on the rack and Brighton took a deserved lead when Matt O’Riley, who has been out injured since his debut following a move from Celtic, burst through an exposed defence to beat keeper Ederson five minutes later.
Brighton earned the reward after passing up a number of chances, with Jack Hinshelwood heading straight at Ederson from point-blank range and Georginio Rutter also missing a golden opportunity before City crumbled under the constant pressure.
Man City crack under Brighton pressure
Manchester City’s road to what they hoped would be a recovery from recent setbacks looked to be a smooth one when Haaland rewarded a period of early supremacy with his 12th Premier League goal of the season.
Instead, Brighton took increasing encouragement from the weaknesses in defence of a City side who struggled against a wave of attacks without the composure usually afforded by experienced duo Ruben Dias and John Stones.
City gradually lost their cool and were hanging on well before substitute Joao Pedro emerged from a melee to finally put the Seagulls level.
Without the world-class presence of Rodri in midfield to steady the rocking ship, City are now giving opponents the sort of hope and encouragement they have rarely been offered in recent years, with Brighton’s full-tilt attacking style under Fabian Hurzeler primed to cash in.
It would be nonsensical to dismiss City as title challengers given their history of success but a lack of form – and a long injury list – may well have opened the door to their rivals. The sight of Kevin de Bruyne emerging as a substitute for the closing staged will have lifted sagging morale, though.
Guardiola will hope to use the international break to regroup before they take on Tottenham at Etihad Stadium on 23 November.