Washington took advantage of Miami's bullpen, scoring runs in the sixth, seventh, and eighth innings for their two-run win.
Harper drew walks in the first and third innings, singled in the fifth, and hit a two-run, eventual game-winning homer in the seventh to score Anthony Rendon.
Drew hit a two-out, pinch-hit home run off Bryan Morris in the bottom of the sixth inning to tie the game at two runs apiece.
Koehler faced 26 batters over 5.2 innings. He gave up six hits and five walks for an in-game WHIP of 1.