By Andrew Both
HUMBLE, Texas (Reuters) - Kevin Stadler carded a five-under-par 67 to share the Houston Open first-round lead with Australian Cameron Percy Thursday.
Stadler, whose father Craig won 13 times on the PGA Tour, including the 1982 Masters, said he had hit a rough patch of form recently.
"I was fighting my swing the last week or two but I got around today," Stadler, 30, told reporters.
"I've been hitting it great all year, except these last couple of weeks. I missed the cut at Bay Hill, got here on Sunday and put in a ton of work on the range. It was a little scrappy today but some stuff I can get better."
Percy found his putting touch to shoot easily his best score of the year. He credited a lesson on the greens from fellow pro Greg Chalmers' caddie, Malcolm Baker.
"I spent hours and hours on the putting green Tuesday and Wednesday and it's made a little difference," he said.
Ireland's Harrington made a move with three successive birdies from the 14th, before bogeying the last.
"My round was going nowhere until I hit 14," he said. "I wasn't feeling on top of my game today.
"I'm pleased enough with the score. I didn't hit it very well on the range before I went out and was a little conservative. I made the most of my opportunities when they came around."
Mickelson made a sensational birdie at the par-five 8th, despite taking a penalty stroke after pushing his drive into a water hazard.
After taking a drop, he hit a hybrid club from 245 yards out and then drained a 50-foot putt for birdie.
"It was one of those fluke things," he said. "I was trying to save par and ended up making a long putt."
Fiji's Vijay Singh withdrew after nine holes due to pain in his abdominal muscles.
(Editing Peter Rutherford)