Ernie starts well in Houston
Texas - Kevin Stadler carded a five-under-par 67 to share the Houston Open first-round lead with Australian Cameron Percy on Thursday.
Americans Anthony Kim, Kevin Sutherland, James Driscoll and Vaughn Taylor trailed by a stroke while Phil Mickelson and Padraig Harrington were in a group on 69.
South African Ernie Els was a further shot back after shooting a two-under-par 70.
Last year's champion Paul Casey was unable to defend his title due to a left shoulder injury.
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."
Briton Casey said the injury was unrelated to the torn muscles in his rib cage area that kept him out for nearly three months last year. He said his withdrawal was a precaution ahead of next week's U.S. Masters.
Fiji's Vijay Singh withdrew after nine holes due to pain in his abdominal muscles.
First round scores
67 - Cameron Percy (AUS), Kevin Stadler
68 - James Driscoll, Anthony Kim, Kevin Sutherland, Vaughn Taylor
69 - Padraig Harrington (IRL), Matt Kuchar, Justin Leonard, Phil Mickelson, Bryce Molder, Adam Scott (AUS), Nicholas Thompson, Omar Uresti, Lee Westwood (GBR)
70 - Stuart Appleby (AUS), Ernie Els (RSA), Martin Laird (GBR), Justin Rose (GBR)
71 - Angel Cabrera (ARG), Graham Delaet (CAN), Martin Kaymer (GER), Soren Kjeldsen (DEN), Carl Pettersson (SWE), Charl Schwartzel (RSA)
72 - Alex Cejka (GER), Brenden Pappas (RSA), Brendon de Jonge (ZIM)
73 - Aaron Baddeley (AUS), Greg Chalmers (AUS), Jason Day (AUS), Luke Donald (GBR), Simon Dyson (GBR), Steve Elkington (AUS), Fredrik Jacobson (SWE)
74 - Henrik Bjornstad (NOR), David Lutterus (AUS), Rory McIlroy (NIR), Andrew McLardy (RSA), Geoff Ogilvy (AUS), Andres Romero (ARG), Yang Yong-Eun (KOR) 74--74
75 - Daniel Chopra (SWE), James Nitties (AUS)
76 - Brian Davis (GBR), Matt Jones (AUS)
79 - Nick O'Hern (AUS)
80 - Mathew Goggin (AUS)