Prayad Marksaeng was setting the early pace at the World Golf Championships-Bridgestone Invitational as play got under way at Firestone Country Club in Ohio.
The Thai European Tour Member opened with three birdies in a row, starting from the tenth tee on the tough, 7,400 yard, par 70 South Course.
Marksaeng bounced back from a bogey at his fourth, the par four 13th, with another birdie at the par four 14th.
He was three under par having played six holes, a one shot leader over South Africa's Rory Sabbatini and Tim Clark and Americans Jerry Kelly and Chad Campbell, all of whom were still playing their front nine holes.
Martin Kaymer of Germany and England's Ross Fisher were the leading Europeans of the early starters, both one under par after five holes in a group including India's Jeev Milkha Singh and Americans Justin Leonard, Sean O'Hair and David Toms.
England's Luke Donald gave back a birdie at the par four 11th, his second, with a bogey four at the 12th, while playing partner Graeme McDowell of Northern Ireland was two over par after four holes having had bogeys at his first and fourth holes.
McDowell's compatriot Rory McIlroy, making his debut at Firestone this week, also opened with a bogey as he teed off at the tenth in a star-studded group with defending champion Vijay Singh, who also bogeyed the tenth, and two-time US PGA Tour winner this year Kenny Perry, who began with a par.
Tiger Woods, a six time winner of this event at Firestone and coming off his fourth victory of the year at last week's Buick Open, was set to tee off among the later starters alongside Sergio Garcia of Spain, while World Number Three Paul Casey of England was placed in the following group off the first tee.
A week before he begins the defence of his US PGA title, Ireland's Padraig Harrington was due to tee off in the final group of the day from the tenth tee.