(Sports Network) - Houston ace Roy Oswalt will try to stay on the winning side of things tonight, when he leads the Astros in the second test of a three-game series versus the Washington Nationals at Minute Maid Park.

Oswalt, who owns a 3-3 mark with a 5.57 earned run average in seven starts this season, is 3-0 in his previous four trips to the rubber, and defeated Milwaukee the last time out on May 2. In the 7-4 victory over the Brewers at Minute Maid Park, Oswalt surrendered four runs -- three earned -- and six hits in six innings of work.

The right-hander dropped his first three starts of the 2008 campaign, but has rebounded nicely to pitch at least six innings in the past four outings. Oswalt is 3-1 with two complete games and a 2.45 ERA in eight career performances (six starts) against Washington.

Houston is still unbeaten in May at 4-0 following a 6-5 victory over the Nationals in the series opener on Tuesday. Lance Berkman had a career night with a 5-for-5 performance at the plate and scored the game-winning run in the eighth inning thanks to an RBI double by Carlos Lee. Berkman had two doubles, three singles, four runs scored and an RBI, while Lee finished with three hits and three RBI in Houston's fourth straight win.

Astros reliever Doug Brocail got the win despite giving up Austin Kearns' go- ahead homer in the eighth. Jose Valverde pitched a perfect ninth for his seventh save innings after starter Shawn Chacon battled through seven frames, yielding four runs on eight hits and four walks with eight strikeouts. The Astros were coming off a three-game sweep of the Milwaukee Brewers at home.

Kearns put Washington on top for a brief moment with a solo blast in the eighth inning. He and Ryan Zimmerman both finished with a pair of hits and an RBI for the Nats, who had a two-game winning streak stopped but lost for just the second time in eight contests. Aaron Boone and Nick Johnson both went deep in a losing effort.

Nationals relief pitcher Luis Ayala absorbed the loss for giving up two runs on three hits in just an inning of work. Starting pitcher Shawn Hill allowed three runs on eight hits and four walks in his 5 1/3 innings of work.

Still searching for a win this season is Nationals starter Odalis Perez. He is 0-3 with a 3.18 earned run average in seven starts this season, and has posted three consecutive no-decisions.

Perez last toed the rubber on May 1 versus Pittsburgh, allowing just a pair of runs and three hits in a season high seven innings of a 3-2 victory. Perez, who is 0-2 in three road starts for Washington, is 0-1 with a 2.16 earned run average in his previous four starts.

The veteran southpaw hasn't fared too well throughout his career against the Astros. Perez is 0-4 with a whopping 12.91 ERA in six career games (five starts) in the series.

Washington went 5-2 against Houston last season, with a 3-1 record at Minute Maid Park.