(Sports Network) - The Houston Astros try to stay unbeaten in the month of May this evening, when they will attempt to complete a three-game sweep of the Washington Nationals at Minute Maid Park.

Houston won its eighth straight home game and fifth in a row overall on Wednesday, as Carlos Lee singled in Kaz Matsui with the winning run in the ninth inning to boost the Astros to a 4-3 victory.

Lance Berkman continued his hot hitting, going 2-for-3 with a pair of walks and a solo home run for Houston, which is in the midst of its longest streak at home since winning nine in a row from July 8-30, 2005.

Over his last three games, Berkman has reached base 13 times, including a franchise record-tying eight straight hits.

Roy Oswalt, who also drove in two runs for Houston, did everything but earn the win on Wednesday. The ace pitcher hurled seven innings and yielded three runs on six hits and two walks. Oswalt also struck out a season-high nine batters for the Astros, including the first seven batters that he retired.

Jose Valverde (4-1) tossed a perfect ninth inning to notch the win, whiffing one in the effort.

Washington's Joel Hanrahan (0-2) did not allow a hit through 2 1/3 innings of work, but he did issue five walks, and was responsible for the decisive run that scored after Jesus Colome came on in relief.

Ryan Zimmerman belted a pair of home runs and finished 3-for-4 with three runs batted in for the Nationals, who have dropped back-to-back contests after winning eight of 10.

Getting the call for the Astros tonight will be right-hander Brandon Backe, who is 2-3 with a 4.42 ERA. Backe picked up the win on Saturday against Milwaukee, as he gave up two runs and five hits in 5 2/3 innings but walked five for the second straight start. He also contributed to the effort with a home run at the plate.

Backe has faced the Nats twice and is 1-1 with a 3.75 ERA against them.

Washington will counter with left-hander John Lannan, who was roughed up by the Pittsburgh Pirates in his last trip to the hill. Lannan was tagged for six runs (five earned) and six hits in three innings by Pittsburgh on Friday, as he fell to 2-3 while having his ERA raised to 3.74.

Lannan defeated the Astros the only other time he faced them, surrendering three runs and five hits in five innings last August.

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