Adam LaRoche struck the go-ahead RBI single in a three-run eighth inning as Washington overcame Philadelphia, 5-3, in the opener of a three-game series on Friday.
Anthony Rendon and Ian Desmond both knocked in a run during the deciding frame for the Nationals, while Tyler Moore contributed a solo homer among his two hits and scored twice.
Stephen Strasburg worked the first six innings, allowing six hits and three runs with five strikeouts.
Mike Adams (1-1) took the loss, charged with three runs on as many hits while failing to retire a batter. It ruined another solid outing from starter Cliff Lee, who gave up four hits and one earned run over seven frames.