Belliard’s two-run homer capped a five-run first. Zimmerman hit an RBI double and a sacrifice fly.
Three players had one RBI each, Austin Kearns had three hits, while three players had two hits for the Nationals, who won three times in the four-game series.
Winner John Lannan (2-2) yielded three earned runs and five hits in five innings.
Closer Chad Cordero recorded his 28th save despite giving up two runs in the ninth.
Houston’s Carlos Lee hit a pair of two-run homers and an RBI single for five RBI. Lance Berkman knocked in Houston’s other run. Lee had three hits and Hunter Pence had two hits for the Astros, who have lost six of 10.
Houston starter Juan Gutierrez (0-1) gave up six earned runs and 11 hits in five innings.