HOUSTON -- Infielder Oswaldo Navarro, who had his contract purchased after the Astros released Kaz Matsui late Wednesday, joined the club Thursday and was eager for another shot at the Major Leagues. Navarro appeared in four games with Seattle in 2006 and was 2-for-3.

"I think I was too young when I got to the big leagues the first time," Navarro said. "I have more experience and more at-bats, and I have a good mental side working for me and more concentration. That helped me put up some good numbers at Triple-A."

Navarro, 25, hit .312 with four doubles, one triple, three homers and 19 RBIs in 20 games for Triple-A Round Rock. He had a .418 on-base percentage and a .506 slugging percentage, but the thing the Astros like about him is his versatility. He can play shortstop, second base and third base.

"His best position probably right now might be second, but at the same time he's very versatile and gives us more options to make more switches," Astros manager Brad Mills said.

Mills was limited with his options prior to the team cutting ties with Matsui, a switch-hitter who can play only second base.

"Any time you have more options the last two or thee innings of the ballgame, that's big," Mills said. "[Navarro] was playing shortstop very well down there. We saw him at third base and second base at Spring Training and we know he's got the ability to play those positions."

Astros' lineup begins to stabilize

HOUSTON -- Now that Jeff Keppinger is entrenched as the Astros' starting second baseman and manager Brad Mills appears to have found comfort in the three, four and five spots in the order with Lance Berkman, Carlos Lee and Hunter Pence, there may be less lineup combinations than there were early in the year.

The Astros had used 36 different lineups through 40 games, mostly because of the unstable catching situation and the alternating of Kaz Matsui and Keppinger at second base. Matsui was released Wednesday and is out of the picture.

"There haven't been as many changes lately," Mills said. "We're going to continue to have changes at catching, but that's settling down."

That being said, Mills admitted some of the regulars are in need of some scheduled games off in the coming days. Berkman hasn't had a day off since April 30, and Lee has started every game since April 24.

"We need to get some of the extra guys in there as much as we can as well," Mills said.

Astros face share of top-tier pitchers

HOUSTON -- Beginning with Thursday's series finale against Colorado in which they faced National League Cy Young contender Ubaldo Jimenez (7-1), the Astros faced four starting pitchers with a combined record of 21-3.

The Tampa Bay Rays, who open a three-game series Friday at Minute Maid Park, will throw Matt Garza (5-1) on Friday, Jeff Niemann (3-0) on Saturday and David Price (6-1) on Sunday against the Astros. It's especially daunting because the Astros began Thursday ranked last in the NL in average, runs, hits, homers and RBIs.

"I don't want to blame it on that, but at the same time there's a lot of good pitchers out there, and we're getting our share of them," Astros manager Brad Mills said.

Already this season, the Astros have faced Tim Lincecum, Barry Zito and Adam Wainwright twice as well as Roy Halladay, Chris Carpenter and Josh Johnson once.

Berkman feels bad about Matsui's release

HOUSTON -- First baseman Lance Berkman said he felt partly responsible for the Astros' releasing of veteran second baseman Kaz Matsui on Wednesday. Matsui was hitting .141 and had struggled at the plate all year, but Berkman said if the Astros' sluggers were doing their part the move might not have been necessary.

"I feel like if I'm playing how I feel like I'm capable and the team is doing better, maybe something like that doesn't happen," Berkman said. "I'm not saying that's the reality of the situation, but you certainly feel that way."

Berkman, the longest current tenured member of the team, entered Thursday hitting .234 with four homers and 13 RBIs. He has seen dozens of players come and go in his career, and he says it's never easy when a veteran player near the end of his career is released.

"The thing that stinks about the business of sports and just from a personal standpoint when the team doesn't do well and when you don't do well personally you feel responsible, not just for yourself, but for other people," he said. "It seems that kind of thing is certainly more prevalent when things aren't going the way everyone thinks they should. We all have a feeling of affection for Kaz, and I certainly feel bad and feel partly to blame for his release."

Worth noting

The Astros have used only five starting pitchers this season through their first 40 games, which is the deepest the team has gone into a season using five starters since 1999. Houston went the first 79 games with Shane Reynolds, Mike Hampton, Jose Lima, Sean Bergman and Chris Holt in the rotation before Scott Elarton started game No. 80. ... Left-hander Tim Byrdak, on the disabled list since May 4 with a hamstring strain/disk irritation, will begin a rehab assignment on Friday in Triple-A Round Rock. He'll pitch one inning Friday and Sunday and could be activated Tuesday.