Webb Simpson carded a sizzling 64 to take the first round lead at the WGC Bridgestone Invitational at Firestone Country Club.
Simpson's fast start in Ohio saw him end the day one shot in front of Open runner-up Henrik Stenson of Sweden.
It's then a shot back to world number one Tiger Woods, defending champion Keegan Bradley, Ryan Moore and England's Chris Wood, who all posted four-under 66s.
Starting from the 10th, 2012 US Open champion Simpson had gone to the turn in 31 with birdies at the 13th, 15th, 17th and 18th and made it four birdies in succession when he picked up shots at the first and second.
A bogey at the third halted his charge briefly before further birdies at the sixth and seventh, but a superb round ended on a disappointing note with a bogey on the ninth.
Stenson had no such concerns after a flawless 65 that began with a birdie at the first and eagle at the par-five second, with the Swede picking up further shots at the 11th and 12th.
The 37-year-old, who finished three shots behind Phil Mickelson at Muirfield last month, has not played in the limited-field event since 2010, when he finished dead last in 80th place.
"In 2010 I played here with pneumonia I didn't know about. Saved Tiger from finishing last though, which I'm sure he appreciated," Stenson joked.
Woods finished joint 78th on that occasion but has also won seven times at Firestone and carded an opening 66 which featured a flawless inward nine of 31.
That was a feat matched by Bristol's Wood, who prepared for the event at his home course of Long Ashton and expressed his thanks to greenkeeping staff by leaving some "cider vouchers" behind the bar.
Compatriots Ian Poulter and Lee Westwood, both third in the Open in differing circumstances, carded rounds of 69 and 71 respectively.
Rory McIlroy played well in patches during a level par 70 but his five birdies were wiped out by three bogeys and a double at the 10th.
"I saw a lot of good signs out there," said the Northern Irishman, who defends his US PGA crown at Oak Hill next week.
Open champion Phil Mickelson looked flat in his first event since lifting the Claret Jug at Muirfield and had to settle for a two-over 72.