City took the lead in the 16th minute when Leroy Sane picked out Brazilian full-back Danilo, who then comfortably slotted past a helpless Matthew Ryan.
Brighton then levelled the game up in the 20th minute, after Davy Propper got in behind to meet an onrushing Claudio Bravo and then he then crossed the ball for Leonardo Ulloa to head in.
With just over ten minutes of the half left, City went back in front when Sane cross picked out Bernardo Silva just inside the right side of the box and he hit a powerful low effort into the bottom right corner.
Pep Guardiola's side then wrapped up the game with 18 minutes left, as a corner was played short to Sane, who was allowed to run into the box and cut it back for Fernandinho to slot into the bottom left corner.
Get forward more
Obviously, with the opposition being City many people may wonder how you can get forward more, but Brighton needed to get forward more.
This is due to the simple fact when they did they caused City problems.
The goal was a prime example as Propper, spotted a gap to run into and committed to and then forced Bravo to come to try and deal with it leaving Ulloa to header into an empty net.
Another good example was in the 58th minute when Brighton put a ball into the box which pinballed around before falling to Anthony Knockaert just six yards out, but unfortunately, he could only fire over the bar.
Apart from that, there was not much to really get excited about in term of going forward for the Seagulls and their travelling fans.
Lewis Dunk and Shane Duffy were superb again
Despite conceding three goals both of Brighton's centre half's were impressive.
The pair made ten or 11 vital blocks during the game, to stop the margin of victory being a lot greater.
Dunk and Duffy threw themselves in front of everything they possibly could have and put their bodies on the line to deny City, but unfortunately, they could not get the clean sheet they really deserved due to a mixture of persistence and patience build-up play from the home side and a couple of individual mistakes.
By individual mistakes, the Seagulls have to fix lapses in concentration similar to the third goal of the night where Knockaert was meant to pick up Sane and cut off the short corner.
However, instead, he decided to leave Sane unmarked and from there the situation could not be rescued.