The visitors were looking to avoid losing successive Premier League games under Pep Guardiola for just the fourth time and were immediately on the front foot here.
A joint-league-high nine goals have been scored in the opening 15 minutes of City’s games this term, but clear-cut chances were hard to come by despite their early dominance.
Savinho was first to threaten an opener, as he forced a smart low stop from Bart Verbruggen after being slotted in by Mateo Kovacic.
The Croatian international was unpicking the Seagulls’ defence at will, and when he slotted in Erling Haaland at the half’s midway point, the striker made no mistake. Though Verbruggen denied his first effort, Haaland was quickest to react to slam home his fourth goal in as many meetings.
The Norwegian could’ve had a hat-trick before the break, yet found himself denied by Verbruggen before heading over from a Phil Foden corner.
Brighton were on the ropes and struggling to get out of their own half, but capitalised on City’s grip loosening before the interval.
Their most promising break came when Kaoru Mitoma surged down the left and fed the in-form Danny Welbeck, but his effort was blocked by a sliding Josko Gvardiol.
Brighton looked to continue that momentum following the restart, with Carlos Baleba introduced by Fabian Hurzeler in an effort to shore up their midfield.
And the contest was certainly more even than the first half, with the hosts disappointed not to be level when Pervis Estupinan’s pinpoint cross was met by a towering Jack Hinshelwood, but his header was too close to Ederson, who kept it out.
Estupinan delivered another dangerous cross soon afterwards which was headed over by Georginio Rutter, while Savinho curled wide at the other end as both sides pushed forward.
However, there was no doubt that it was Brighton who were on top, but making their chances count was proving difficult as substitute Joao Pedro dragged an effort wide.
By the time Bernardo Silva and Kevin De Bruyne were introduced beyond the 70-minute mark, City had failed to register a shot on target in the second half, and their staunch rearguard was eventually breached by Pedro, who slammed home from close range after a scramble on the six-yard line.
City’s implosion was complete just five minutes later, as a slick Seagulls move culminated in Pedro slotting in Matt O’Riley to score on his Premier League debut and seal a famous win for Brighton, who move into the top-four after opening their league campaign by going six matches unbeaten on their own turf.
The result is disastrous for City, meanwhile, as they could be five points adrift of early pacesetters Liverpool by the end of the weekend.