Astros 6, Pirates 4

KISSIMMEE, Fla. -- The injuries are piling up for the Houston Astros at the wrong time.

Staff ace Roy Oswalt was removed after four innings of work on Friday due to a slight left hamstring strain, but the Astros got a walk-off, two-run home run from Chris Johnson in the bottom of the ninth to salvage a 6-4 win over the Pittsburgh Pirates.

The Astros rallied from a 2-0 deficit with a four-run eighth inning, but the Pirates tied it in the top of the ninth with two runs. Chris Shelton doubled with two outs and Johnson followed with a towering shot over the center field wall off reliever Jeremy Powell to win it in the bottom half.

Oswalt would be the fourth everyday player the Astros have had go down in the last few weeks. First baseman Lance Berkman (knee surgery), outfielder Michael Bourn (oblique strain) and shortstop Tommy Manzella (strained quadriceps) are all dealing with injuries as well.

Houston general manager Ed Wade said the team will send Oswalt back to Houston to be examined by team physician, Dr. David Lintner, Friday night or Saturday morning.

Wade said Oswalt first experienced pain on the same side after his start against the New York Mets on Sunday was rained out. Oswalt pitched an inning when the rain forced him back to the batting cages. A few pitches into the bullpen session he felt some discomfort and shut himself down.

"I just want to get him checked," Wade said. "Head colds concern me. Allergies concern me this time of spring training. Since it's the same leg and had two things now occur, we're going to get him to Houston and let Dr. (David) Lintner look at him."

Oswalt said this is the first time in his career that he's had any trouble with his hamstring.

Houston manager Brad Mills said the original plan was for Oswalt to throw 85-90 pitches and hopefully five or six innings in his third start of the spring.

"This late in camp, there's always a concern," Mills said. "The one positive thing is that he wanted to go back out. He felt that little strain in his hamstring, but he wanted to go back out there. That means he's concerned about it but he's not so scared about it that he's willing to go out there and pitch."

Oswalt acted as if nothing was wrong when he talked with reporters after the start and had no idea that the team was sending him back to Houston to be examined.

"I felt a little tight in the cage, nothing major," he said about Sunday's BP session. "Today, I didn't feel anything. The hammy got a little tight toward the end, but I told them I could go a couple innings more. But it's spring training. It's nothing major. If I needed to pitch seven, I think I could have gotten through it. There's no pain."

Oswalt gave up one run on three hits over four innings and struck out six against the Pirates before his early exit. He struck out the side in the third. The Pirates broke his streak of 9 2/3 scoreless spring innings in the fourth when Jeff Clement singled in a run.

Oswalt has pitched only 10 innings thanks to a pair of rainouts, saying the weather has thrown off his rhythm.

Pirates starter Zach Duke was masterful on the mound and at the plate Friday. Duke kept the Astros scoreless through 6 2/3 innings and only allowed three baserunners while striking out two in his fourth and longest start of the spring.

Duke also slapped a pair of doubles, including one off of Oswalt in the third.

Game notes
Astros RHP Brett Myers said he felt better after sustaining a strained left groin Thursday in his start against the Phillies. Myers isn't expected to miss his next scheduled start. ... OF Michael Bourn appeared in a minor league game on Friday, his first action since he injured his oblique during batting practice on March 18. ... The Astros trimmed their spring roster to 38 Friday by optioning reliever Wesley Wright to Triple-A Round Rock, and reassigning pitcher Shane Loux and infielder Oswaldo Navarro to minor league camp. ... Pirates closer Octavio Dotel, who has made just one appearance this spring due to a strained oblique, struck out three while recording five total outs against the Yankees' Triple-A team at Pirate City on Saturday.