Four of the Mets' runs were unearned thanks to three Milwaukee errors. New York snapped a two-game skid.
Nieuwenhuis drew a bases-loaded walk in the first, singled in two runs in the second, added an RBI single in the fourth and finally tripled home a run while the Mets were scoring three times in the ninth.
New York built a 7-2 lead in the fourth inning and also came up with three RBI from Juan Lagares.
Zack Wheeler (2-1) survived five innings to pick up the win. He gave up three runs on seven hits with three walks. Johnny Helweg (0-3) was roughed up for seven runs, only three of which were earned, on seven hits in 3 2/3 innings.