Washington - Former US Open champion Webb Simpson shook off a weather delay to fire a career-best 61 on Thursday, grabbing a one-shot lead over Kim Whee after the first round of the US PGA Tour Greenbrier Classic.
Simpson was within striking distance of a 59 on the Old White TPC course in White Sulphur Springs, West Virginia, but admitted he tried not to think too much about it.
"It's hard, because I'm trying to take it one shot at a time, make every shot the same as any other shot," said Simpson, who has struggled since winning the Players Championship earlier this year.
Simpson had come back from a weather delay of almost two hours with birdies at 14 and 16 that moved him to nine-under on the par-70 course.
A poor second shot at the par-five 17th, where Simpson ended up in the rough, helped doom his chances at achieving golf's magical number.
"That didn't really give me a chance to get at that left pin," Simpson said. "When you're coming in from that left rough to that pin you're not expecting to get close.
"It's kind of a bummer to end the round that way but overall a great, solid round," added Simpson, who had seven birdies and chipped in from just off the green for eagle at the par-five 12th.
South Korea's Kim saw a streak of four straight birdies from the second through the fifth end with back-to-back bogeys.
But he rebounded with five birdies in his next seven holes, finishing with a total of 10 birdies on his way to an eight-under round - his best ever on the PGA Tour.
Chilean 19-year-old Joaquin Niemann was a further stroke back on seven-under 63 with Kelly Kraft on 64.
Niemann set the early pace with his 63 on a course where he fired a 64 in the final round last year as an amateur.
He teed off on 10 and birdied six of his first 10 holes, capping his round with a birdie at the ninth.
"I made a couple of good birdies in the start of the round," he said. "After that I thought I was going really low. My game was feeling really good and my putter was good. So all my game was good today."
Former major winner Keegan Bradley headed a group of players on 65, while five-time major winner Phil Mickelson headed a big group on four-under 66.
Mickelson, 48, is playing his first tournament since the US Open - when he drew criticism for intentionally violating the rules of golf by hitting his ball when it was still moving on the green.
Mickelson, who was penalized two strokes but escaped disqualification, later apologised.
Leading first-round scores on Thursday in the US PGA Tour Greenbrier Classic in White Sulphur Springs, West Virginia (USA unless noted, par-70):
61 - Webb Simpson
62 - Kim Whee (KOR)
63 - Joaquin Niemann (CHI)
64 - Kelly Kraft
65 - Keegan Bradley, J.J. Henry, Jason Kokrak, Chad Campbell
66 - Steve Wheatcroft, Tom Hoge, Austin Cook, Xander Schauffele, Ryan Moore, Billy Hurley, Ollie Schniederjans, Harold Varner, Robert Streb, Dou Zecheng (CHN), David Lingmerth (SWE), Kevin Chappell, Phil Mickelson, Brandt Snedeker, Stephan Jaeger (GER)