HOUSTON -- Quality starting pitching and a revamped bullpen are carrying the Nationals through their injury woes, and facing the challenge of an opponent as talented and injury-ravaged, Washington got more of the same to maintain its positive momentum.

Tanner Roark recovered from a shaky start, and the Nationals delivered extra-base hits with two outs in consecutive innings to claim a 4-3 interleague win over the Houston Astros on Tuesday night at Minute Maid Park.

Roark (10-8) pitched into the sixth inning after dealing with early traffic before handing over a one-run lead to his bullpen, with four relievers responding to the challenge of protecting it.

The Astros (76-49) mounted their biggest threat in the bottom of the eighth, loading the bases with one out against right-hander Brandon Kintzler, recently acquired from the Twins. Max Stassi followed by grounding into an inning-ending, 5-4-3 double play, with second baseman Daniel Murphy having the time to nab Stassi with the throw despite double-clutching.

"He certainly saved the game," Nationals manager Dusty Baker said of Kintzler. "We needed a double play and turned a very, very near double play. That was a close call at first base that was right on time."

The Nationals (75-48) first struck with two outs against Astros right-hander Charlie Morton (10-6) in the third inning. Howie Kendrick drilled a two-run triple to center field that scored Matt Wieters and Michael Taylor, who beat out a double play by hustling down the line.

Wieters socked a two-run home run to center, his ninth homer on the season, in the fourth to erase a one-run deficit and set the table to Roark to get rolling and the bullpen to deliver again.

Left-hander Sean Doolittle notched his 12th save with Washington, throwing a perfect ninth.

Houston struck for a solo run in each of its first three at-bats, doing so with two outs in the first and second. However, an inability to post a crooked number in the third inning proved costly.

Josh Reddick and Derek Fisher delivered two-out RBIs in the first and second innings, respectively, with Reddick plating George Springer for a 1-0 lead and Fisher driving home Carlos Beltran to double the advantage.

After taking a 3-2 lead on another RBI single by Reddick, this one an infield hit that ricocheted off Roark, the Astros loaded the bases with one out. Roark responded by striking out Marwin Gonzalez and inducing a groundout from Carlos Beltran, the first two of 10 consecutive batters he retired to cap his outing.

"They did a good job of winning those spots, especially in the third when we had a little bit of an opportunity, and in the eighth as well," Astros manager A.J. Hinch said. "Those big moments are big swing moments."

When the Nationals scored in the fourth, the Gonzalez strikeout and Beltran groundout loomed large. Roark allowed three runs (two earned) on six hits with seven strikeouts and one walk over 5 2/3 innings.

"I felt like I got a little mad, got a little fight within me and I knew it was going to be a battle right off the bat," Roark said of his closing surge. "So, I just tried to use that to my advantage and just go out them and be aggressive and just make my pitches."

Morton allowed four runs on five hits and one walk with six strikeouts over six innings.

"In retrospect, you look back in those situations, you're in two-out situations," Morton said of the Kendrick and Wieters at-bats. "You don't have to make perfect pitches, but you have some room there to be a lot better than that. I just grooved them two pitches."

NOTES: Astros RHP Will Harris (right shoulder inflammation) pitched one scoreless inning for Double-A Corpus Christi, and the club will evaluate his progress before rendering a decision on his reinstatement from the 10-day disabled list. LHP Tony Sipp and RHP Michael Feliz also worked scoreless innings in their rehab appearances. C Evan Gattis (concussion) has a three-day program with Corpus Christi. ... While Nationals RHP Max Scherzer continues to receive treatment for neck inflammation, the club has not determined if he will be reinstated from the 10-day disabled list on Friday when he is eligible. ... Astros C Brian McCann (right knee soreness) is set for reinstatement from the 10-day disabled list on Thursday and should play in the series finale against Washington. McCann landed on the DL on Aug. 14.