City took the lead in the second minute when Kevin De Bruyne converted David Silva’s cross from the left flank.
They had to wait until five minutes before the break to double their advantage as this time De Bruyne turned provider for Sergio Aguero to hammer home.
Aguero notched his second with another fine finish into the top corner early in the second half before Bernardo Silva concluded the scoring 17 seconds after arriving on the field, plcing a low drive past Mat Ryan.
City at times played within themselves, but have still run out comfortable victors.
Graham Potter will feel that his team did not play that poorly, but were simply outclassed by a quality outfit.
BRIGHTON SUBS: Shane Duffy, Pascal Gross, Alireza Jahanbakhsh, Glenn Murray, Aaron Mooy, David Button, Aaron Connolly.
BRIGHTON (3-4-3): Mat Ryan; Adam Webster, Lewis Dunk, Dan Burn; Martin Montoya, Dale Stephens, Davy Propper, Bernardo; Leandro Trossard, Neal Maupay, Solly March.
MANCHESTER CITY SUBS: Claudio Bravo, Ilkay Gundogan, Angelino, Bernardo Silva, Fernandinho, Joao Cancelo, Phil Foden.
MANCHESTER CITY (4-3-3): Ederson; Kyle Walker, Nicolas Otamendi, Aymeric Laporte, Oleksandr Zinchenko; Kevin De Bruyne, Rodri, David Silva; Riyad Mahrez, Sergio Aguero, Raheem Sterling.