Gio Gonzalez got knocked out in the fourth, and Tampa Bay ripped Washington, 6-1, on Monday.
Gonzalez (4-4) gave up five runs on eight hits in three and a third innings, and left with the Nats down 5-0 after four innings.
That was more than enough for Rays starter Erasmo Ramirez (6-2), who scattered five hits and three walks in six scoreless innings, striking out four.
The loss drops the Nationals (33-31) a game and a half back of the first-place New York Mets in the National League East.