All the focus had been on De Bruyne as the 33-year-old made his 142nd and final appearance at the Etihad Stadium but it was Egyptian Marmoush who stole the spotlight in the 14th minute with a stunning shot which swerved and dipped before going in off the post.
After De Bruyne somehow hit the crossbar in front of an open goal and Evanilson hit the post at the other end, Bernardo Silva doubled City's lead before halftime. Nico Gonzalez got a third in the 89th minute before Daniel Jebbison's consolation.
A mad few minutes in the second half saw both sides reduced to 10. First Mateo Kovacic went for denying a clear goalscoring opportunity when he pulled back Evanilson in the 67th minute - forcing Pep Guardiola to end Belgian star De Bruyne's final home appearance early.
Six minutes later, Lewis Cook followed for an ugly challenge on his replacement Gonzalez.
Bouncing back from Saturday's FA Cup final defeat to Crystal Palace, City moved up to third in the table and a point at Fulham on Sunday should be enough for a top-five finish, but Bournemouth saw their hopes of clinching a European place come to an end.
Elsewhere on Tuesday night, there was no hangover for Cup winners Palace.
Just days after winning at Wembley to secure their first major trophy, the Eagles kept the party going in front of home fans at Selhurst Park.
Eddie Nketiah scored twice in a 4-2 win against Wolverhampton Wanderers, who went ahead through Emmanuel Agbadou.
But two goals from Nketiah in the space of five minutes in the first half put the south Londoners in front.
Chelsea loanee Ben Chilwell's deflected free kick made it 3-1 and Jorgen Strand Larsen's header offered Wolves hope in the 62nd minute.
Eberechi Eze — who scored the winning goal in the final — was on target again late on to set Palace up nicely for their final match of the season at champions Liverpool on Sunday.
With AP.
