The Nationals hit four solo home runs off Cliff Lee Wednesday night en route to a 5-1 win over the Phillies.
Washington hit back-to-back home runs in the fifth and sixth innings to get out to a 4-0 lead on the home team.
The Phillies (45-47) mustered little offense against Gio Gonzalez, who improved his record to 7-3. Gonzalez allowed one run on six hits over seven innings.
Darin Ruf, called up from Triple-A Lehigh Valley earlier this week when Ryan Howard was placed on the DL, produced the Phils' only run of the game when he hit a solo home run in the seventh.
The Nationals (47-44) got home runs from Anthony Rendon and Wilson Ramos in the fifth and from Jayson Werth and Ryan Zimmerman in the sixth.
Lee's record fell to 10-3 with the loss Wednesday night.