Hamels (7-1), the first major league pitcher with seven victories this season, took the mound for the first time since a five-game suspension brought about by his admission he intentionally hit Washington rookie Bryce Harper with a pitch.
It was Hamels' seventh straight victory, following a loss in his season debut April 9.
Shane Victorino had an RBI double in the third and hit a solo shot in the eighth to highlight the Philadelphia offense.
The Phillies ended a four-game skid and also halted Washington's three-game winning streak.
Edwin Jackson (1-2) allowed three runs on seven hits over seven innings to take the loss.
No batters were hit during the game. Harper went 1-for-3 against Hamels with a walk.