Gio Gonzalez goes after his 15th win of the year this evening when the Washington Nationals and San Francisco Giants square off in a battle of National League division leaders at AT&T Park.

Gonzalez went the distance to beat the Houston Astros on Wednesday, as he allowed three runs and nine hits and struck out seven to run his record to 14-6 on the year to go along with a 3.32 ERA.

"Gio couldn't have been any better," manager Davey Johnson said. "He pitched an outstanding ballgame. We hug a lot. I'm going to hug him more. My whole bullpen should hug him. What a great effort."

Gonzalez, who's one victory behind New York's R.A. Dickey and Cincinnati's Johnny Cueto for the NL lead, has faced the Giants four times and is 1-2 against them with a 3.42 ERA.

Washington saw its season-high eight-game winning streak come to an end on Sunday in Arizona, as it dropped a 7-4 decision to the Diamondbacks at Chase Field.

Ryan Zimmerman knocked in a run for the fourth straight game as the Nationals lost for only the second time in their last 11 games. They still lead the National League East by 4 1/2 games, as they eye their first postseason berth since 1981 when the franchise was in Montreal.

"We are going to lose just like every one else loses, but we won the series," said Zimmerman.

Even with Sunday's setback, the Nationals have won 12 of their last 14 road contests and own the best road winning percentage (.639) in the majors.

San Francisco, meanwhile, won in thrilling fashion on Sunday, as Hunter Pence's three-run homer in the eighth inning lifted the Giants over the Colorado Rockies, 9-6.

Trailing 6-4, the Giants loaded the based with no outs in the eighth. Melky Cabrera ripped a grounder up the middle and a diving Josh Rutledge got his glove on the ball but was unable to corral it, allowing Brandon Crawford to score. Buster Posey followed with a game-tying sacrifice fly before Pence ripped a fastball into the seats in left-center field.

"It's not really about me, it's about the win and that was huge," remarked Pence. "A lot of things came together for that opportunity to come up and I think everyone enjoyed it on our team."

Cabrera had two hits and three RBI while Buster Posey, Brandon Belt and Ryan Theriot each drove in a run for the Giants, who won for the fourth time in six games and maintained their one-game advantage over the Los Angeles Dodgers in the NL West.

Clay Hensley (4-3) picked up the win after allowing one run on three hits over two innings of relief. Javier Lopez and Sergio Romo combined for a perfect ninth to secure the win.

Tonight, the Giants turn to righty Ryan Vogelsong, who is 10-5 with a 2.27 ERA. Vogelsong scattered three hits over seven scoreless innings to beat the St. Louis Cardinals on Wednesday, as he earned his third win in four starts.

"I'm just going out there and trying to get outs, trying to go as deep as I can in the game," Vogelsong said.

This will be Vogelsong's first start against the Nationals, but he has faced them four times out of the bullpen and has pitched to a 1.13 ERA in those outings.

Vogelsong may have the added bonus of having Pablo Sandoval back in the lineup tonight. Sandoval has been out since July 24 because of a strained left hamstring. He is batting .299 with eight home runs and 33 RBI on the year.

Washington swept the Giants earlier in the season in D.C.