Francesco Molinari is two shots behind the clubhouse leaders after carding a first-round 67 in the WGC-Bridgestone Invitational at Firestone Country Club.
The Italian started and ended his first nine holes with birdies before collecting two more consecutively from the 14th.
However, a bogey on his penultimate hole meant he failed to keep up with Ryan Moore and Charl Schwartzel at the top of the leaderboard.
A quartet of birdies on the opening nine helped Moore’s cause, with another on the 15th handing him a flawless opening round of 65.
Schwartzel, starting on the back nine, gained a shot on his first hole before producing a stunning display after the turn.
Despite dropping a shot on the first, Schwartzel responded with five birdies in six holes, including four consecutive from the fourth.
Patrick Reed and Brandt Snedeker are locked on three under alongside Molinari.
Reed had initially sat pretty at the top following six birdies, with three in a row from the 11th, but two bogeys in his final six holes saw him settle for a 67.
Rory McIlroy made a solid start to his first event since winning the 143rd Open Championship.
The Northern Irishman, who could reclaim top spot in the world rankings from Adam Scott with his first World Golf Championship event this week, picked up three birdies after starting on the tenth.
But a dropped shot at the third left the 25 year old alongside fellow Europeans Sergio Garcia, Miguel Ángel Jiménez and Jamie Donaldson on two under.
Garcia started well as he attempted to make it third time lucky this week following second-placed finishes at the Travelers Championship and the Open.
The Spaniard, starting on the back nine, looked to be continuing his fine form with two birdies in the first three holes, but a bogey on the third hindered his progress.
His compatriot Jiménez picked up shots twice after the turn while Donaldson impressed on the back nine with a trio of birdies.
Matt Kuchar, starting on the tenth, was in touch with the early leaders after gaining shots on four of his first five holes but struggled afterwards, dropping two shots and also shooting a double bogey on the fourth.
American trio Jimmy Walker, Keegan Bradley and Ben Crane, as well as Australian Marc Leishman, were also two under.
David Howell was the leading European earlier before two bogeys in his final three holes halted his progress and left him one under.
Lee Westwood and Luke Donald struggled and were three and two shots over par after shooting opening rounds of 72 and 73 respectively.