With Karstens looking to win a fifth straight start in this series and a fourth consecutive decision overall, the Pittsburgh Pirates try to extend their winning streak over Houston to eight Friday night at Minute Maid Park.
After missing more than two months with inflammation in his throwing shoulder, Karstens (3-2, 3.52 ERA) was hit hard in his first start since being removed from the disabled list June 25 but has been superb since. The right-hander has gone 3-0 with a 1.86 ERA over his last four outings spanning 29 innings, allowing 19 hits and seven walks.
"I'm not trying to blow fastballs by people; I'm just trying to keep people off-balance, and when they do hit the ball hard, hopefully it's right at us," he said.
Karstens was terrific again Sunday, throwing seven innings of five-hit ball during a 3-0 win over Miami.
"When Jeff is on, he reads swings well, keeps the ball down, works quick, keeps his fielders in play," manager Clint Hurdle said. "And that's what we saw today."
Karstens' recent success shouldn't come as much of a surprise to the Astros (34-66), whom he's defeated five times - his most wins against any opponent. Karstens has been nearly untouchable in winning each of his last four starts in this series, allowing one run and one walk over 30 2-3 innings.
He scattered four hits and struck out a season-high eight in eight innings of a 2-0 win over the Astros on July 5. In his last visit to Houston, Karstens threw a five-hitter for his second career shutout in a 4-0 victory July 15, 2011.
The Astros also failed to get much going against A.J. Burnett during Thursday's series opener, falling 5-3. It was Pirates top prospect Starling Marte, though, who stole the show, homering on the first pitch he saw in his big league debut.
"That was a swing that touched a lot of people," Hurdle added. "Starling has been a special player all the way up. He's been a lot of places and a lot of people have had the opportunity to watch him. We've got an entire minor league system and an academy in the Dominican Republic pulling for him."
The Astros have dropped 23 of 25 overall - including a season-worst 10 in a row by a 72-30 margin. They haven't lost 11 straight since Aug. 17-28, 1995.
"It's hard coming in every day and getting beat; guys are getting (ticked) off a little bit, and they want to come out here and get a win," said Chris Johnson, who hit his seventh homer Thursday. "Tomorrow we are going to have to come out here and do whatever we can to get a win. That is what it has to be."
Houston now turns to Jordan Lyles (2-7, 5.50). The right-hander yielded a career-worst eight runs - five earned - and 10 hits over 5 2-3 innings Sunday in an 8-2 loss at Arizona, dropping to 0-3 with a 7.54 ERA in four starts this month. He surrendered seven runs and nine hits over four-plus innings during an 11-2 defeat at Pittsburgh on July 2.
Lyles, though, has held his own at home, where he's 2-1 with a 2.30 ERA over his last four starts.
Wandy Rodriguez, who spent his first seven-plus seasons with Houston before getting traded to Pittsburgh on Tuesday, will take the mound against the Astros on Saturday.