Marcum (11-3) allowed one run on six hits and a walk for Milwaukee, which bounced back from a 5-1 loss to the Dodgers to win for the seventh time in eight games.
Casey McGehee went 3-for-4 with two RBI, while Prince Fielder had two hits, scored two runs and knocked in a pair of the victors.
Mike Pelfrey (6-10) took the loss after yielding four runs — three earned — on eight hits and four walks in a five-inning start.
The Mets were coming off a series win at San Diego and were welcomed back to Citi Field by storm that resulted in a two-hour, 46-minute delay.
After waiting out the rain, Milwaukee jumped in front during its first at-bat. David Wright couldn’t handle a hard grounder to third by Ryan Braun, who stole second and was brought home on Fielder’s single to center field.
Fielder came up in the fifth with runners on the corners and slapped a base hit to left field to make it 2-0. McGehee added an RBI single and Yuniesky Betancourt doubled past a diving Wright to knock in Fielder.
D.J. Carrasco relieved Pelfrey in the sixth and gave up a pair of two-out runs, one coming on his wild pitch. McGehee singled in the other run.
The Mets finally got to Marcum in the seventh when Jason Pridie doubled off the right-field wall and Josh Thole knocked him in with a single.
Kameron Loe relieved Marcum in the eighth and struck out Wright to leave a runner on second, and Frankie De La Cruz hurled a scoreless ninth to close out the win.
Braun was ejected in the third inning by home plate umpire Angel Campos for arguing balls and strikes…Marcum has won four straight decisions…Brewers manager Ron Roenicke turned 55 on Friday.,.Milwaukee improved to 27-36 on the road.