Also lurking was Dustin Johnson, who threw away careless shots but was still only five shots out of the lead.
McIlroy remains a work in progress. He started slowly, not giving himself many birdie chances and hitting tee shots some 20 and 30 yards short of Johnson and Keegan Bradley. But the 23-year-old from Northern Ireland made birdie on the par-5 15th, followed with an 18-foot birdie on the 16th, and then cut loose with a tee shot that was some 20 yards beyond where Johnson hit his drive.
That wasn't an accident. McIlroy tends to hold back early in his round until he gets more comfortable with his scoring.
"The game is fickle," he said. "You make a couple of birdies, a few good shots, and your confidence goes up. A few bad ones, and it goes down a bit. I hit a couple of drive, and 17 is a good example, when I let it go and it's fine. It gets out there."
McIlroy said he hasn't played enough tournaments to get into that groove, and he was at least happy to have two more chances at the Houston Open. He headed to the practice range after lunch, and then decided to make sure he played some more by signing up for the Texas Open.
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