Akron - Former US Open champion Webb Simpson set the early pace and his six-under 64 held up to take the first-round lead at the Bridgestone Invitational on Thursday.
Despite a bogey on his final hole, the par-four ninth, Simpson finished with a one-stroke lead over Sweden's Henrik Stenson, whose round included an eagle at the par-five second hole.
World number one Tiger Woods was among a group of four players sharing third place, two strokes off the lead at the Firestone Country Club.
Woods, a seven-time winner of the event, was joined at four-under by England's Chris Wood, Ryan Moore and defending champion Keegan Bradley - who had four birdies and no bogeys.
Jim Furyk, Luke Donald and Rickie Fowler - who all notched runner-up finishes in the event - posted three-under 67s and shared seventh place with Jason Dufner, Bubba Watson and Bill Haas.
Woods's effort included six birdies and two bogeys. He hit 10 of 14 fairways and all but two greens in regulation.
"It was a little blustery today," Woods said. "Wind was up, greens were soft. But at least the ball was flying. And even though it was a little more wet because of the rain, with it being this warm, the ball is still traveling."
Phil Mickelson, teeing it up for the first time since winning the British Open, carded a two-over par 72.
"I certainly didn't want to shoot over par and leave myself this far back after the first day," Mickelson said. "But my game feels sharp. I feel like I'm rolling the ball well. Tomorrow if I can just mentally see it a little clearer, I should have a good day."
Northern Ireland's Rory McIlroy, who will defend his PGA Championship title next week, recovered from a double bogey six at the par-four 10th to finish at even par 70 for the round.
Simpson, the 2012 US Open champion, is playing the Bridgestone for the first time. He qualified last year, but didn't play because of the birth of his second child.
Simpson rolled in a 17-footer for his first birdie of the day at the 13th, drained a 20-footer for another at 15, and launched a run of four straight birdies at 17.
Simpson cooled off with a bogey at the third, but he added birdies at six and seven -- sinking a 30-footer at the sixth -- before capping his round with a bogey at the last where he missed the green.
"Did a lot of things well today and made a lot putts," Simpson said. "Just played really good solid golf. I missed a couple left today with some iron shots, so I've got something to work on, even on days like today."
Stenson opened with a birdie, then drained a 31-footer for eagle at the second.
He landed his approach two feet from the pin for a birdie at 11, and birdied the par-three 12th from within three feet.
"Birdie-eagle start, you can't get any better than that," said Stenson, who didn't have a bogey. "I feel I'm playing nicely and just doing my job on every hole."
Leading first-round scores on Thursday in the World Golf Championships Bridgestone Invitational (USA unless noted, par-70)
64 - Webb Simpson
65 - Henrik Stenson (SWE)
66 - Ryan Moore, Chris Wood (ENG), Tiger Woods, Keegan Bradley
67 - Jason Dufner, Bubba Watson, Rickie Fowler, Bill Haas, Jim Furyk, Luke Donald (ENG)
68 - Scott Piercy
69 - Kiradech Aphibarnrat (THA), Ian Poulter (ENG), Paul Lawrie (SCO), Zach Johnson, Justin Rose (ENG)
70 - Harris English, Gonzalo Fernandez-Castano (ESP), Jonas Blixt (SWE), Ken Duke, Peter Hanson (SWE), Richard Sterne (RSA), Satoshi Kodaira (JPN), Francesco Molinari (ITA), Jamie Donaldson (WAL), Rory McIlroy (NIR), Paul Casey (ENG), Branden Grace (RSA)
71 - Matteo Manassero (ITA),Nick Watney, Bo Van Pelt, Graeme McDowell (NIR), Lee Westwood (ENG), Miguel Angel Jimenez (ESP), Steve Stricker, Sergio Garcia (ESP), Ernie Els (RSA), David Lynn (ENG)