(AFP) - William McGirt opened up a record three-shot opening round lead but world No. 1 Jason Day and No. 2 Jordan Spieth were also in the hunt at the WGC-Bridgestone Invitational on Thursday.
McGirt set a tournament record for the largest first-round lead by firing a six-under 64 as he aims for his second win in Ohio in just four weeks.
McGirt won the Memorial Tournament in Dublin, Ohio in a play-off in early June for his first USPGA Tour victory.
Australia's Day shot a three-under 67 and is tied for second with Emiliano Grillo and Jimmy Walker at the Firestone Country Club course in Akron, Ohio.
Spieth is one stroke behind Day with a 68. He is tied with three others - Anirban Lahiri, Charley Hoffman and Rickie Fowler.
Dustin Johnson, who is fresh off his first Major championship win at the US Open, is also lurking near the top of the leaderboard after shooting an even-par 70. He is tied with Japan's Hideki Matsuyama and England's Paul Casey.
McGirt, who is making his World Golf Championship debut, made six birdies and finished off his round with a 45-foot par save.
Spieth made several nice par saves to remain close to the leaders. He hit just one green in regulation on the front nine.
Spieth then closed with four birdies. He needed just 21 putts during his round and chipped in for par at No. 8.
Johnson's round included two birdies and one bogey. Johnson is tied with Billy Hurley, who won the Quicken Loans National tournament last week.
Defending champion Shane Lowry, who finished in a tie for second at the US Open two weeks ago, stumbled to a six-over 78.