The hosts took the lead through Kevin De Bruyne with just over a minute played as David Silva cut the ball back for him to score a simple goal, and City maintained their dominance throughout the rest of the game.
Sergio Aguero then scored either side of half time - the second a sublime strike - to take the game well and truly away from the visitors.
Substitute Bernardo Silva sealed the victory in the 79th minute, slotting home from the left just over a minute after coming off the bench.
City got off to a flying start as a slick move that saw Oleksandr Zinchenko slide a ball down the left for David Silva, who evaded his man and got to the byline before squaring to De Bruyne to fire into an empty net and put the hosts up with barely a minute played.
Aguero then fired wide from a tight angle and Riyad Mahrez struck an effort too close to Mat Ryan as City continued to dominate, with Graham Potter's side unsure whether to stick or twist after conceding so early in the game.
De Bruyne went very close to a second shortly after as he hit a stinging low drive just wide of the left post from the right before David Silva squandered a brilliant chance to make it 2-0.
Raheem Sterling beat his man on the left before squaring for the onrushing David Silva, who somehow scuffed his shot wide of the far post from close range when it looked easier to score.
Pep Guardiola's side suffered what could be a significant blow in the title race, however, as Aymeric Laporte had to be stretchered off after sustaining an injury when fouling Adam Webster - a challenge the Frenchman actually received a yellow card for.
Fernandinho made his first appearance of the season, coming on to replace Laporte in an unfamiliar centre-back role, but City's flow was not affected by the loss of their star defender.
City's pressure eventually told as Mahrez pulled off a clever backheel for De Bruyne and continued his run to drag defenders away while the Belgian found Aguero in the box, and the Argentine kept his cool, waited for Brighton's defenders to commit and stuck the ball in the back of the net at the near post.
Brighton's lone bright spark in the game was Leandro Trossard, who managed to cause City problems in the final third.
The best of his chances came shortly before half time when Bernardo's dinked cross evaded Kyle Walker and left him one-on-one with Ederson at the back post, only for the Man City keeper to thwart his first-time effort.
City could have been 3-0 up at the break but Aguero opted not to shoot and squared for Mahrez in the box - there was the suggestion of a foul, but nothing was given and the chance went begging.
However, Aguero made amends and ended the game as a contest with the moment of the match 15 minutes into the second half.
The Argentine received the ball on the edge of the box from David Silva in a fairly central position and struck a sweet, dipping effort into the top-right corner of the goal, giving Ryan no chance of saving it.
Substitute Bernardo Silva put the icing on the cake, tucking home from the left after the irrepressible Aguero found him in space just moments after he had replaced David Silva in midfield.
The win means that City extend their unbeaten run against Brighton at home to 10 matches in all competitions, with six wins in a row.
MANCHESTER CITY (4-3-3): Ederson; Walker, Otamendi, Laporte (Fernandinho 37'), Zinchenko; Rodri, De Bruyne (Gundogan 69'), D. Silva (B. Silva 78'); Mahrez, Aguero, Sterling
BRIGHTON & HOVE ALBION (5-4-1): Ryan; Montoya, Webster, Dunk, Burn, Bernardo (Connolly 66'); March, Stephens, Propper, Trossard (Gross 74'); Maupay (Murray 67') body check tags ::