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HOUSTON -- Don't feel too sorry for the young Astros. A slew of rookies is helping Houston's future seem a bit brighter.

Rookie Henry Sosa allowed two hits and struck out seven over six innings, Matt Downs got his league-leading 12th pinch-hit RBI and the Astros rallied for an 8-2 win over the Pittsburgh Pirates on Tuesday night.

Sosa was one of six rookies in the starting lineup that helped push the Astros to their sixth victory in seven home games.

Sosa got his second straight major league victory. J.D. Martinez drove in three runs, giving him 28 for the month -- the most for an Astros rookie in any calendar year and third all-time for NL rookies in August. Jose Altuve hit his second major league homer and drove in two runs.

What they started in the minor leagues, they are continuing at the major league level.

"It's no doubt when a guy comes up, especially from Double-A, he has some guys he's familiar with," Astros manager Brad Mills said. "J.D. was with us for a while in spring training.

"At the same time, he spent the first four or five months with those guys. When he came up here it's good to have someone you know. All that breeds unity."

Altuve homered in the fifth against Charlie Morton (9-8) to tie it 2-2 and the Astros broke loose with six runs in the sixth on seven hits -- a season-best for an inning.

Downs pinch hit for Sosa and singled to left for the go-ahead run. Altuve added an RBI single, Martinez drove in two runs with a single, and Carlos Lee and Jimmy Paredes also had run-scoring hits in the inning.

"We are pushing each other all the time trying to make each other better," Martinez said. "We are confident. We have that confidence that we can tell each other, 'What are you doing. Let's go.' We've played with each other so long. We want nothing but the best for each other. It's nice to have."

Sosa walked Ronny Cedeno to start the third inning. Cedeno was sacrificed to second and scored on Alex Presley's long single to center.

Martinez also had an RBI hit in the seventh. He went 3 for 5 to lead Houston's 13-hit attack.

"They do have a young club now, those guys are really fighting," Pirates manager Clint Hurdle said. "They're pitching better, they are getting timely hits, they are executing off the mound, and now they have had a big inning on us in both games in this series."

Andrew McCutchen homered off Brett Myers in the ninth. McCutchen became the eighth player in Pirates history to get 20 homers and 20 stolen bases in the same year.

"It's good to be able to say that I got there," McCutchen said. "We still have a lot of ball to play, and I am just going to continue to go out there, play hard and try to finish up strong."

Morton had faced 338 right-handed batters without allowing a home run before Altuve's blast. He pitched 5 1/3 innings, allowing four runs on six hits.

"I think I pitched pretty well until the sixth inning," Morton said. "I think I was mixing up pretty well. My location wasn't the best -- and it hasn't been. But at the same time, maybe I should be pitching for more strike outs instead of trying to be really fine."

Game notes

Myers pitched the final two innings. His wife Kim is expecting a child later this week and Myers likely will miss his next start. He is scheduled to return to the rotation on Tuesday. ... Houston has never lost more than 97 games, a franchise mark it has matched three times. The Astros last lost 97 games in 1991, and they also did it in 1975 and 1965. ... Pittsburgh has 84 extra-base hits in August, third most among NL teams. ... The Pirates have lost eight of their last nine road games. ... Pittsburgh's James McDonald (8-6) faces Houston's J.A. Happ (4-15) in Wednesday's game.