Not much has been able to slow down Washington's pitching staff lately, though.
Harper had surgery Tuesday on his left thumb that he injured sliding into third base in a win over San Diego on Friday. He joins catcher Wilson Ramos (left hand surgery) and third baseman Ryan Zimmerman (broken right thumb) on the disabled list.
The Nationals (15-12) still are among the NL leaders in runs, though, after winning the first of this two-game series 4-3 on Tuesday. Adam LaRoche's RBI double in the eighth tied it before he drove in Denard Span for the go-ahead run with a single in the ninth.
'When I'm feeling pretty good, one, I'm taking some walks and two, I'm using the whole field,'' LaRoche said.
Jayson Werth homered to improve his average to .387 during a seven-game hitting streak.
Gio Gonzalez struck out nine over six innings before three relievers kept the Astros (9-18) scoreless the rest of the way. Washington has a 2.12 ERA over its last 11 games, allowing three earned runs or fewer eight times.
Zimmermann (1-1, 4.05 ERA) looks to help that trend continue as he seeks another solid outing. He's 1-1 with a 2.70 ERA over his last three starts after allowing three runs in six innings of Washington's 4-3, 12-inning loss to the Padres on Thursday. He threw 91 pitches, though, and felt he should have been able to make better pitches to go deeper into the game.
"I had really good stuff and everything was working," Zimmermann said. "It's just unacceptable to be going six innings with the stuff I had. It's just frustrating (when) you throw 90-some pitches and two aren't where you want them to be. It kind of sums up your night right there."
The right-hander is 1-2 with a 3.70 ERA in four career starts against the Astros. He tied his career high with 11 strikeouts while giving up three hits in six innings of a 5-0 win the last time he faced them Aug. 9, 2012.
Houston will counter with Brett Oberholtzer after it failed for the third time this season to win three straight.
Oberholtzer (0-4, 4.61) had a 3.04 ERA over his first four starts, receiving just six runs of support as the Astros lost each. He didn't help his own cause Thursday though, giving up six runs and eight hits in 3 2-3 innings of a 10-1 loss to Oakland.
The left-hander is 0-8 over his last nine outings, but he had a 2.87 ERA in that stretch prior to Thursday. The Astros' offense has provided him with an average of 1.78 runs since his last victory on Sept. 1.
"I wouldn't say (it felt) weird, but I guess it's something new," Oberholtzer said of his struggles in his latest outing. "It's baseball, and I get an opportunity to work at all of it tomorrow. This won't stop me going forward."
Oberholtzer has never faced the Nationals, who have won five straight and nine of the last 10 meetings.