Aguero had the first half-chance of the match in the sixth minute when he produced a spectacular overhead kick, but Shane Duffy was on hand to make the block.
Duffy and fellow central defender Lewis Dunk continued to impress in the period that followed as a number of crosses into the Brighton box were headed clear by the duo.
City made the breakthrough less than two minutes later, however, with Sterling having the simple task of tapping a low Sane cross into the back of the net from close range.
The home side continued to dominate the possession, but serious opportunities were few and far between in what was a largely uneventful first half.
City's final two chances of the first period came for Sterling and Fernandinho, but the England international saw his powerful effort beaten away by Ryan before the latter also found Brighton's goalkeeper in good form.
Sane was next to come close for City just before the hour, as the German headed a Bernardo Silva cross over the crossbar from close range, before Ryan made a wonderful save to keep out a powerful David Silva drive.
City did double their advantage in the 65th minute, however, when Aguero raced away from a number of Brighton shirts in a central position before feeding Sterling, and the attacker returned the favour to allow the Argentine to slide into the back of the net from close range.
Riyad Mahrez twice had attempts after entering the field as a substitute, but his first effort was wide of the target before Ryan made a smart save 15 minutes from time.
Brighton made three changes in the period that followed, but City continued to dominate as they closed in on their sixth Premier League win of the campaign.
It was not a vintage performance from the home side, although they were always comfortable against a Brighton team who only managed one attempt on target, and had just 21% of the ball.
MAN CITY (4-3-3): Ederson; Walker, Otamendi, Laporte, Zinchenko; Bernardo Silva, Fernandinho, David Silva (Foden 88'); Sterling, Aguero (Jesus 66'), Sane (Mahrez 71')
BRIGHTON (4-4-1-1): Ryan; Montoya, Dunk, Duffy, Bong; Knockaert (Jahanbaksh 79'), Propper, Kayal, March (Izquierdo 83'); Bissouma; Locadia (Murray 73')