Seeking a seventh victory in eight matchups between the clubs this season, visiting Washington tries for its first sweep of Houston in 12 years Thursday night.
The Nationals (68-43) are 6-1 in the season series with the Astros (36-76), but the last five of those victories have all come by one-run margins.
After posting back-to-back extra-inning wins to open this four-game set, Washington escaped with another narrow victory Wednesday, prevailing 4-3. Having overcome a shaky first inning, Gio Gonzalez withstood Houston's rally attempt in the ninth to throw his second career complete game. Gonzalez's first ever homer - a two-run shot - also proved key given the Nationals' 1-for-12 effort with runners in scoring position.
"Gio couldn't have been any better," manager Davey Johnson said. "He pitched an outstanding ball game ... it was just a great outing by him to save the bullpen."
Seeking to match a season high with a sixth consecutive victory overall, the Nationals franchise hasn't swept the Astros in a series of at least three games since May 19-21, 2000, when the club was the Montreal Expos. It's never completed a four-game sweep of Houston.
Looking to help the Nationals do just that is Jordan Zimmermann (8-6, 2.45 ERA), who's 5-0 with a 1.65 ERA over his last eight starts. The right-hander, though, was knocked around and didn't receive a decision during Saturday's 10-7 win over Miami, yielding a season-high five runs - four earned - and seven hits over five innings.
While Zimmermann is 0-2 with a 4.91 ERA in three career starts in this series, he scattered four hits over seven innings of one-run ball April 18 during Washington's 3-2 victory. His two losses to the Astros have both come at Minute Maid Park, where he owns a 7.15 ERA.
Zimmermann will be opposed by Lucas Harrell (9-7, 3.98), who's led Houston to its only two victories in the last 22 games. Looking to win a career-best third consecutive start, Harrell has gone 3-2 with a 2.26 ERA over his last eight outings - yielding two runs or fewer in all but one of them.
He issued a career high-tying five walks Saturday but managed to limit the damage, allowing two runs and four hits over six innings of a 3-2 win at Atlanta.
"I got away from my strengths and started nibbling a little too much at the end," said Harrell, who carried a shutout into the sixth. "It got me in trouble walking guys. I felt like my changeup really bailed me out in a couple of situations."
In his only previous start against Washington, Harrell gave up one run and four hits over 6 2-3 innings opposite Zimmermann in April. The right-hander is 6-1 with a 2.02 ERA in nine home starts.
He'll need to be wary of Michael Morse, who singled Wednesday to extend his career-best hitting streak to 17 games. The Nationals' slugging first baseman is batting .315 with three homers over that stretch.
Bryce Harper, in contrast, hasn't been able to get much going at the plate of late. The 19-year-old phenom is 0 for 11 in this series and isn't expected to be in Thursday's lineup.
"He's pressing a little bit," Johnson said. "I'll give him the day off ... and let him regroup a little bit."