William McGirt fired a six-under-par opening round of 64 to establish a three-shot lead in the first round of the WGC-Bridgestone Invitational in Ohio.
McGirt won his first PGA Tour title at the Memorial Tournament in the same state earlier this month to climb up to 46 in the rankings.
And the 37-year-old American was in fine form at the Firestone Country Club in Akron on Thursday, sinking six birdies in a bogey-free round.
McGirt told PGA Tour Radio afterwards: "This course is like Muirfield. I love it, it fits my eye well - apart from the 18th, I can't work out how to hit the fairway.
"I'm comfortable on older style golf courses and I love the look of this one. I know I can compete out here and I know I can win it."
Compatriot Jimmy Walker, world number one Jason Day and Argentinian Emilio Grillo were his nearest pursuers, with Jordan Spieth, Rickie Fowler, Charley Hoffman and India's Anirban Lahiri a shot further adrift.
Justin Rose was the best placed Briton, sharing ninth, on one under. The Englishman bird ied three of his first five holes but was not able to maintain the momentum in the early stages of a tournament brought forward from its usual August slot because of the Olympics.
Andrew Johnston dropped three shots but also made three birdies for an opening-round 70 to finish on level par, alongside another Englishman - Paul Casey.
Scotland's Russell Knox, who still harbours Ryder Cup hopes, was in a share of 51st position after a round of four over.
However, defending champion Shane Lowry - coming off his best finish at a major - struggled in the first round. The Irishman, who tied for second in the US Open, could only manage a six over par 76.
Source: PA
