LaHair did not play in the Cubs' final four Cactus League games because of a bulging disc in his back. On Thursday, he was able to run and hit in the batting cage.
"It's just such a minor thing, but it's something I couldn't prevent -- it's like a nerve thing," said LaHair, who blamed an impingement for the pain in his back and leg. "The nerve settled down now and the pain is pretty much out, and now it's just getting back into the feel of things. I should be back in there this weekend."
LaHair has had something like this before and it settled down in three days. He said he did not expect to need to go on the disabled list. He also wasn't that concerned about the bulging disc.
"I bet 90 percent of hitters in baseball have that," LaHair said.
What's tough is LaHair, 29, has not made an Opening Day roster the last five years, and this was finally his chance.
"I've been preparing myself mentally the past few days just to be ready," LaHair said. "The most important thing is to not go backwards, and keep going forward and keep getting better. Once I'm better, I should be good to go.
"Today was a really good day, and I've been making huge gains each day, a lot faster than [the training staff] anticipated," he said. "Today was exceptional, because I did some running, I hit in the cage. My swing felt good in the cage."
Baker has been used primarily as a sub at second, third and the outfield, but did play a lot of first base this spring. It's not his first Opening Day start; he also started the opener in 2005 with the Rockies, at third base.
"It's just another game, and I'm obviously a litte more excited for this one," Baker said of Thursday's start.