The Astros (76-67) are 2-7 against Pittsburgh (60-82) this season, although the Pirates are just 28-40 against the NL Central. Houston, however, comes in having won 10 of 11, which has moved it back into postseason contention. With 19 games remaining, Houston is in fourth place in the wild card standings, six games behind the Milwaukee Brewers.
Right-hander Alberto Arias (0-0, 2.63 ERA) will pitch in place of Backe on Monday in his first major league start.
Arias was acquired off waivers from the Rockies on July 31. He is 1-0 with a 3.43 ERA in 18 appearances over two seasons with Colorado. In 12 relief appearances this season, he's allowed four runs and 12 hits in 13 2-3 innings of work.
Ian Snell (6-10, 5.59) counters for the Pirates.
Snell is 2-1 with a 3.13 ERA in his last four starts. He pitched six innings last Tuesday to beat Cincinnati, allowing two runs - one earned - in a 3-2 victory.
The right-hander is 0-0 with an 8.10 ERA in two starts against the Astros this year.
Ty Wigginton, who led the majors in homers and slugging percentage in August, is expected to miss eight to 10 days after straining his left groin in Saturday's 2-0 win over the Rockies.
"We'll just have to wait and see," Astros manager Cecil Cooper said. "Groins are pretty difficult."
Wigginton, batting leadoff for the first time since Aug. 22, was trying to beat out an infield single in the first inning and was forced to take a long stride as he hit the bag. He couldn't beat the throw and hobbled off the field.
"It happened about halfway there, and just at that point I tried to get long," Wigginton said. "Once I felt it, I just tried to get there."
Wigginton is hitting .294 with 22 homers and 55 RBIs. He has started in left field in 20 of 27 games since Carlos Lee suffered a broken finger and has been a key to the Astros' recent surge.
"He takes a lot out of our offense right there when you don't have him in there, particularly against left-handed pitching," Cooper said.
With 19 games remaining, Wigginton is determined to get back on the field at some point this month. However, he's never strained a groin and isn't sure how long the recovery process will be.
"It is disappointing," he said. "I guess anytime you pull a muscle or tweak a muscle or whatever it is, it's different from if you break something.
"If you break something, there's nothing you can do about it, but with a pulled muscle, you feel like there's something you can do. I was ready to go and ran extra sprints (before Saturday's games). It's just one of those things."
ASTROS 7, ROCKIES 5: Darin Erstad and David Newhan came off the bench in the eighth inning delivered consecutive RBI hits to lead the Astros to a come-from-behind win at Colorado. The Astros won for the 10th time in 11 games to get to nine games over .500 (76-67). They have the best record in baseball since the All-Star break at 32-16.
--RHP Brandon Backe will miss his scheduled start Monday against the Pittsburgh Pirates at Minute Maid Park after suffering tightness in his forearm near his elbow.
Backe, who is 9-12 with a 5.44 ERA in a career-high 162 2/3 innings in 29 starts, will be replaced by RHP Alberto Arias, who had a 1.52 ERA in eight games (three starts) for Class AAA Round Rock this year.
Backe, 30, felt discomfort in the forearm in the second or third inning of his start Tuesday in Chicago. The arm felt worse after he threw in the bullpen Saturday, but Backe said Sunday he feels his arm is getting tired.
"It just seems like it hasn't really recovered too much from that point on to the bullpen (session) I threw (Saturday)," Backe said. "Throwing my bullpen, I didn't really feel too bad, but it was after my bullpen it started to get sore again.
"I wanted to maybe try and make the start, but just analyzing it and looking at the situation it's probably best I go ahead and miss this start and see how it feels."
Coincidentally, Sunday was the two-year anniversary of the surgery Backe underwent to repair the ulnar collateral ligament in his right elbow. He came back to pitch in five games at the end of last season before making every start this year.
"I'm not too worried about it," he said. "Obviously, I don't want to miss a start. I hadn't missed one yet, and that was the whole plan. I do have to understand I have put a lot of work on a newly reconstructed elbow.
"Sometimes we feel like we're super human and we'll get through it, but I have to realize I haven't pitched this much in my career and if it feels tender the last thing I want to do is have another surgery and go through more rehab. The way I feel now, I feel like I should miss this start and see how it feels by mid-next week."
Backe will try to get back on the mound in the bullpen in a few days with hopes of rejoining the rotation.
"This has definitely opened my eyes up more than the other times," he said. "I'm trying to be honest with them and letting them know I don't feel really good right now.
"I want them to know my arm is getting tired. I don't want to miss the start, but don't want to press it too far. The ultimate decision was made by (manager Cecil Cooper) that I was going to be skipped, and I agreed with him. It's OK with me."
--LHP Wandy Rodriguez left after one inning Sunday at Colorado with a right oblique strain, the same injury that forced him to leave his previous start a week earlier.
"I felt it in the bullpen a little bit, but not too much," Rodriguez said. "When I faced a hitter I tried to throw hard. In the bullpen I threw nice and easy and not too hard, but in the game I threw hard and I felt it a lot."
--RHP Geoff Geary, who hasn't pitched since Aug. 26 because of a strained right groin, threw two innings of 25 pitches each in a simulated game Sunday and believes he's close to being able to return.
"I'll see how I feel (Monday) and if I'm OK I'll be ready to go Tuesday," Geary said. "I feel worn out, to be honest with you. Fifty pitches? That's like a four-inning thing for me. I definitely got my work in today."
--RHP LaTroy Hawkins, also bothered by an oblique injury, returned to the mound Sunday for the first time since Aug. 31 and threw a scoreless inning.
--2B Kaz Matsui missed his 54th game of the season Sunday because of injury, and manager Cecil Cooper has no idea when he will return. Matsui is taking batting practice and fielding groundballs, but Cooper said it's not at the same intensity as game action.
"When he feels like he's 90 percent, he has a chance to play." Cooper said. "We're not there yet. We'll have to keep monitoring until he's ready to rock and roll."
Matsui has been on the disabled list three times, most recently for an irritated disk in his back. He was activated Tuesday when rosters expanded but still hasn't played.
--RHP Jose Valverde worked the ninth inning Sunday for his NL-leading 40th save, extending his club record for consecutive appearances with a save to 13. He's four shy of Billy Wagner's club single-season saves record.
BY THE NUMBERS: 12 -- Consecutive appearances by Astros closer Jose Valverde with a save, a club record.
QUOTE TO NOTE: "It does seem like when we need to put together an unbelievable winning streak we can do it. A lot of that is due to the fact we've gotten great starting pitching, and you can't have a streak like this without throwing the ball well, and they've thrown the ball exceptionally well." -- 1B Lance Berkman, on the team's pitching during their eight-game winning streak that ended Sept. 5, during which Astros pitchers posted a 1.95 ERA.