Hefner (4-6) turned in a dominating 105-pitch performance, yielding just a solo homer to Jonathan Lucroy and a second-inning single to Sean Halton. The right-hander allowed one walk and struck out eight.
Josh Edgin recorded the first two outs of the eighth inning and Bobby Parnell notched a four-out save, his 15th of the season, as the Mets took two-of-three contests in Milwaukee.
Josh Satin went 3-for-4 with an RBI as the Mets scored single runs following errors by Brewers third baseman Juan Francisco in the fourth and sixth innings.
Tom Gorzelanny (1-2) absorbed the loss, surrendering just the two unearned runs on eight hits over six full frames.