Zimmermann lasted six innings, yielding four runs on eight hits. He walked none and struck out four. Since starting the season 3-1, Zimmermann has gone 2-4 in his last six starts.
His solo home run to left off Carlos Zambrano in the third inning staked the Nationals to a 1-0 lead. But Logan Morrison tied it with a solo shot in the fifth.
Zimmerman's two-run double made it 3-1 in the fifth, but the Marlins took the lead for good in a three-run sixth that featured a two-run home run by Giancarlo Stanton.
Zambrano worked six innings, allowing three runs on seven hits, walking two and striking out five. Heath Bell got the final three outs for his eighth save.
Washington continues its nine-game road swing with a Tuesday night game against the Marlins. Washington's Edwin Jackson (1-2, 3.38 ERA) will face Miami's Anibal Sanchez (2-3, 2.87 ERA) in a battle of hard-luck pitchers