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09/10/09 8:30 PM ET

Astros' injuries open door for Johnson

Rookie gets first start as Keppinger sits with sore back

HOUSTON -- Jeff Keppinger's ailing back kept him out of the starting lineup Thursday and created an opportunity for Chris Johnson to make his first Major League start at third base.

Keppinger, who's been out since Friday with tightness in his back, was originally penciled into manager Cecil Cooper's lineup Thursday against the Braves, but Keppinger told head athletic trainer Nate Lucero he couldn't start after testing his back by running.

"I still hadn't tried to run yet, and when I did the back was bothering me," Keppinger said. "The pounding would send little jolts in my back, and I tried to go out there and run and still felt it. Talking with Nate, he said the best thing to do is take another day."

Johnson made his Major League debut when he pinch-hit for injured third baseman Geoff Blum in the fifth inning Wednesday. He wound up going 0-for-2. Johnson, who hit .281 with 13 homers and 42 RBIs at Triple-A Round Rock, batted seventh in the lineup Thursday.

"I'm anxious to play today," he said. "Yesterday I was nervous about playing, and today I was just anxious. It's the big leagues, so mentally it's different. But it's the same game."

Blum is likely out for the rest of the homestand after he suffered a bruised shin and a mild left ankle strain trying to break up a double play in the third inning Wednesday. He was shuffling around the clubhouse Thursday wearing a protective boot on his right foot.

"It's badly bruised and he has the ankle sprain on top of that, so we'll give him a few days," Cooper said.

Brian McTaggart is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.