Ryan was kept busy in the opening half but managed to repel everything Pep Guardiola’s men threw at them.
That included one incredible save just after the half-hour mark to keep out Brazilian star Gabriel Jesus.
Sergio Aguero’s cross was perfect for Jesus who looked certain to score with a head from just six yards out but Ryan somehow clawed it away with a superb reflex stop.
It took almost 70 minutes for City’s class to eventually tell.
Kevin De Bryune and David Silva combined to set up Aguero to finish, giving Ryan no chance with a powerful shot from inside the box.
Then just five minutes later, a cross from the right was headed past the Aussie keeper by his own defender Lewis Dunk to put the result to bed.
While it was disappointment for Brighton, Ryan was excellent in his EPL debut and he’ll be between the sticks again next week as they travel to play Leicester City.