In their first Premier League match Chris Hughton’s men withstood waves of pressure until Aguero’s 70th-minute strike and an own goal by Lewis Dunk five minutes later.
City almost opened the scoring when Gabriel Jesus’s 34th-minute header was saved by Mathew Ryan.
When Jesus did score, his effort was disallowed for a handball.
Aguero had a chance on 51 minutes but shot wide after Shane Duffy’s underhit backpass.
Brighton twice came close through Duffy and Davy Propper, but Aguero made the difference.
De Bruyne dispossessed Dale Stephens and David Silva slipped the striker in to score.
Dunk headed Fernandinho’s cross into his own goal under pressure from Jesus to seal the points.