(My Sportsbook) - A pair of last-place teams start up a three-game series tonight at Nationals Park, where the Houston Astros make their first appearance at the new venue to take on the struggling Washington Nationals.

Houston enters the nation's capital with a 42-50 overall record, the worst among National League Central clubs, and has lost seven of nine games to begin the month of July. Washington is in even worse shape, having compiled a poor 35-58 mark thus far, and heads into this set having dropped seven of its last eight matchups.

The Astros do come in on a positive note, however, as the team avoided a three-game sweep in Pittsburgh with Wednesday's 6-4 decision over the Pirates. Kaz Matsui, in his first game back from a stint on the disabled list, had an RBI double for Houston during a two-run seventh inning that snapped a 4-4 deadlock.

Geoff Blum belted a three-run homer in the first inning for the Astros, while both Ty Wigginton and Michael Bourn finished 2-for-5 with a run scored. Matsui, who had been sidelined with a strained right hamstring, also collected a pair of hits on the evening.

Brian Moehler (5-4) notched the win after working the first six innings and allowing four runs on seven hits. Chris Sampson followed with two scoreless frames in front of closer Jose Valverde, who shut the Pirates out in the ninth to record his 23rd save of the year.

Houston is 2-4 thus far on a nine-game road trip and 20-29 as the visitor this season.

The Astros hope to be buoyed by tonight's return of ace Roy Oswalt. The standout right-hander missed his last turn in the rotation due to a strained left hip and a nerve problem in his lower back, injuries that forced him to exit a June 30 start against Los Angeles after six innings.

Oswalt was terrific before leaving that game, as he limited the Dodgers to one run on six hits and racked up nine strikeouts to lead the Astros to a 4-1 win. The 30-year-old did throw a bullpen session on Tuesday and came through without any setbacks.

The three-time All-Star is 3-1 with a 2.63 earned run average in nine games (7 starts) against the Washington/Montreal franchise. Oswalt faced the Nationals in Houston on May 7 and permitted three runs while striking out nine in a seven-inning no-decision.

Oswalt will be opposed tonight by former teammate Tim Redding. The Washington right-hander began his pro career in the Houston organization and pitched four seasons with the Astros from 2001-04.

Redding is now in his second season with the Nationals and has posted a 6-3 record with a respectable 4.06 ERA through 19 starts this year. He has not received a decision in any of his last nine outings, but Washington has gone 7-2 in those nine Redding starts.

The 30-year-old pitched well enough to win this past Saturday in Cincinnati, where he held the Reds to one run on eight hits over six innings. It marked the third time in his last five starts that Redding has surrendered two runs or less.

Redding faced the Astros twice last season, producing a win and a loss while yielding just three runs over a span of 14 innings.

After snapping a six-game losing streak with Wednesday's 5-0 home win over Arizona, the Nationals failed to sustain the momentum in last night's series finale with the Diamondbacks. Stephen Drew hit a go-ahead RBI double in the top of the 11th inning and Arizona tacked on another run later in the frame to come away with a 7-5 decision.

Washington extended the game by scoring in both the bottom of the ninth and 10th innings. The Diamondbacks put up three runs in the top of the 10th to grab a 5-2 lead, but a Willie Harris single and Austin Kearns' two-run double drew the Nationals back even.

The Nats sent the game into extras when Arizona third baseman Mark Reynolds misplayed a ball off the bat of Kearns, which allowed two runners to cross the plate.

Kearns ended with three RBI in the loss, while Nationals All-Star Cristian Guzman finished 3-for-5 with a run scored.

Luis Ayala (1-5) was dealt a defeat after giving up two runs on three hits in the top of the 11th. Washington starter Jason Bergmann permitted only two runs on six hits over the first seven innings.

Houston won two of three matchups with the Nats at Minute Maid Park back in May, but Washington is 9-4 in its last 13 clashes against the Astros. Houston has also lost five of its last six in D.C.