Williamson's homer was his third in five games since being recalled from the minors Friday, when Hunter Pence was placed on the disabled list. Belt has five homers and seven RBIs during his hitting streak.

Michael Taylor hit a three-run homer and Moises Sierra had two hits for the Nationals, who have lost four in a row and five of six.

Washington threatened in the eighth inning, when Howie Kendrick doubled off Sam Dyson with one out. The Giants intentionally walked Bryce Harper, the potential go-ahead run, before Ryan Zimmerman grounded into a double play.

Right-hander Reyes Moronta (1-0) gave up one hit in two scoreless for his first major league victory as the Giants won their second consecutive series after winning none of their first six.

Hunter Strickland pitched the ninth for his fifth save, his third in as many days. Giants starter Ty Blach gave up four hits and three runs in five innings. He struck out three and walked two.

Tanner Roark (1-2) gave up six hits and four runs in six innings, striking out four and walking two. He entered the game 6-0 with a 2.02 ERA in seven career appearances against the Giants. He was 4-0 as a starter vs. San Francisco, having given up three runs in 27 innings.

The Giants took a 1-0 lead in the first inning when Joe Panik scored on Roark's bases-loaded wild pitch by Roark. Belt's two-out, two-run homer in the third inning after a Panik single made it 3-0.

Zimmerman walked and Sierra singled with two outs in the fourth inning before Taylor tied the game with a three-run homer off Blach, who had retired 11 of the first 12 batters. Blach has given up two homers in 31 1/3 innings this season.

Williamson, who had two hits, hit a two-run homer in the Giants' 4-2 victory in the first game of the series Monday. It was measured at 464 feet, tied for the fourth longest in the majors this season.

--Field Level Media