A rampant display in the opening 45 minutes saw the Premier League champions pick up all three points in the south coast, with Phil Foden grabbing a brace against Graham Potter's men.
Ilkay Gundogan opened the scoring for the vistiors early on after an error by Brighton keeper Robert Sanchez, and Jack Grealish setting up Foden to make it two shortly after.
There was some debate as to who would claim City's third, which was eventually awarded to Foden after Gabriel Jesus' initial shot deflected off the 21-year-old past Sanchez into the net.
However, Brighton enjoyed a bright spell after the interval as City put their foot off the gas and allowed the Seagulls a few decent chances at getting back into the tie.
"They (Brighton) have all the mechanisms of a big team. I know it from playing against Swansea when Graham (Potter) was there and last season, they always tried to play, I admire (them) for that," said City boss Pep Guardiola following the win.
Brighton pulled one back with less than ten minutes left on the clock, with Alexis Mac Allister netting from the spot. Guardiola added: "Not a top four team, but they (Brighton) play like one. That's why they know how difficult it is, and a big compliment for our team."
Despite the late scare, City put the tie to bed in stoppage time with Foden teeing up Riyad Mahrez to make it four for the Sky Blues, who face West Ham in the Carabao Cup on Wednesday evening.
Guardiola added: "We saw what they (Brighton) do, we figured out maybe we have the space, because when they play man to man, they have one man free - just the keeper.
"They (Brighton) are incredibly aggressive, when the passes are more than 5-10 metres, they win it after. Most importantly, when they have the ball, they know exacly what to do, not just defend well and after channels.
"They (Brighton) occupy the space really good. That's why you have one more man in the middle, they occupy pockets well, know the spaces, they make runners from outside, highs and wide that don't allow the fullbacks."
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