The game featured eight home runs, three of them by Washington's Ryan Zimmerman and two from Davis.
Zimmerman drove in four runs with his solo shots in the first and fourth innings and his two-run blast in the fifth. He doubled his home run total this year to six.
The last of Zimmerman's long balls gave Washington a 6-2 lead, but the Orioles got one run back in the sixth on a homer by Nick Markakis and they then swept from behind by batting around in the seventh.
Ryan Flaherty led off the inning with a single against Jordan Zimmermann (8-3) and Steve Pearce followed with a home run to left.
Nate McLouth next came up with an infield single and scored the tying run on Manny Machado's double, which drove Zimmermann from the mound.
Markakis continued the barrage with a single off Tyler Clippard that brought home Machado and Davis hit his homer to right for the final runs of the game.
Davis also hit a solo shot in the fourth.