The Seagulls – who had won just one of the previous 15 head-to-heads this century – saw an early Danny Welbeck chance saved.
From then on, though, it was one-way traffic, as after Nathan Ake had poked a Phil Foden free-kick off target, the visitors took the lead when Kevin De Bruyne converted with a magnificent diving header, meeting Kyle Walker’s cross and arching his neck to nod into the top corner from deep in the penalty area.
Foden soon made it 2-0 after controversially winning a free-kick 20 yards out, dusting himself down to net with a heavily-deflected strike that wrong-footed Jason Steele after hitting Pascal Gross on the back.
The England international then doubled his tally minutes later, clinically finding the bottom corner after Bernardo Silva had won possession when the hosts criminally tried to pass their way out of their own box.
Roberto De Zerbi made a couple of half-time substitutions, and as a result the game was a little more even after the break.
The Citizens were still able to create a plethora of chances though, including a thumping Julian Alvarez shot that was too close to the goalkeeper, but the Argentine did not have to wait too long to strike, ending a 10-game Premier League goal drought when converting into an empty net having been teed up by Walker.
There was worse to come for Brighton, who were left furious when Joao Pedro was not awarded a penalty, despite seemingly being tripped in the box by Josko Gvardiol.
Even so, that would only have been a consolation strike as the hosts’ winless run extended to five matches, further damaging their hopes of climbing into the European spots.
Despite the wide margin of victory for City, their goal difference is eight worse off than Arsenal’s, yet a perfect record in the remaining matches will see them crowned champions regardless.
Flashscore Man of the Match: Phil Foden (Manchester City)
