American Bryson DeChambeau holds the clubhouse lead after darkness curtailed round one of the US PGA Championship at a testing Oak Hill in New York.
DeChambeau carded a four-under 66 to lead Scottie Scheffler, Dustin Johnson and Corey Conners by one.
Masters champion Jon Rahm and England’s US Open winner Matt Fitzpatrick both struggled and signed for six-over 76s.
Unheralded American Eric Cole is top of the leaderboard on five under but the 34-year-old has played only 14 holes.
Cole will return, along with 11 other groups, at 07:00 local time (12:00 BST) on Friday to finish his round. England’s Justin Rose will also be out early and his first shot will be a 20-foot birdie putt on the 15th to get to two under.
Former Masters champions Adam Scott and Dustin Johnson were among the later starters. They challenged for the lead and got to four under before both dropped shots on the 18th as they raced to complete their rounds in near darkness.
Johnson carded his first bogey of the round to finish on three under while Australian Scott ended on a disappointing two under after a double-bogey six at the last.
DeChambeau, who famously bulked up before outmuscling Winged Foot – a course likened to Oak Hill – to win the 2020 US Open, certainly seemed comfortable with six birdies and just two bogeys in his opening round.
Rory McIlroy, who has won this title twice, battled illness to shoot 71, one better than defending champion Justin Thomas.
The start of the 105th US PGA Championship was delayed for one hour and 50 minutes because overnight frost covered the course in Rochester, which is in western New York state, close to the Canada border. But when play started, this iconic and difficult track soon turned up the heat.
Patience and positioning is key at Oak Hill, with thick rough gobbling up any shots that stray off line, making it almost impossible to find and hold greens when digging the ball out.
While many players had a frustrating day, Scheffler was the epitome of calm, as is his usual demeanour, and he managed to navigate the menacing par-70 layout without dropping a shot in his round of 67.
It was a first bogey-free round in a major, in his 15th start, and coming at such a notoriously difficult course gave the 2022 Masters champion even more delight in his efforts.
“This is one of those places where you just try and stay in position, make the important par putts and just keep the momentum going. I did a good job of that,” he said.
“I feel like my game is better suited for this kind of test. I get more excited for a tournament like this versus a birdie-fest like last week. With that being said, I don’t think mentally I would be able to handle playing a tournament like this every single week on Tour.”
McIlroy was a subdued figure in the build-up, with the Northern Irishman still hurting from his stinging missed cut at the Masters, and that continued onto the course with three bogeys in a scratchy front nine.
The four-time major winner showed creditable fight on his back nine though with three birdies against one bogey to keep himself in the contest at one over – all the while being slightly under the weather himself.
“I’m fighting something,” McIlroy said. “But I actually feel better today than I felt yesterday, so plenty of water and a bit of rest, I’ll be fine.”
It was a disappointing start for Rahm though, with the Spaniard looking strangely out of sorts as he laboured to a 76 to leave him thinking more about making the cut than winning the title.
He birdied his first hole, the 10th, but did not pick up another shot until the eighth, to bookend a round that featured six bogeys and a double bogey.
England’s Fitzpatrick, who was in the final pairing at last year’s US PGA, also struggled to a 76, carding three bogeys on each nine as he failed to find a single birdie.
American Thomas only really made a couple of mistakes, but they cost him three shots as he finished on two over par, while his good friend Jordan Spieth was another who let his temperature boil over at times during his round of 73.
Spieth was a doubt for the tournament with a wrist injury, but showed no real signs of that troubling him as he made a wobbly start to his latest bid to claim the only major to have so far eluded him and with it complete the career Grand Slam.
Canadian Conners and 2011 US PGA champion Keegan Bradley are both tremendous iron players so it was no huge surprise to see them both challenging on a course where positioning is everything.
Norwegian Viktor Hovland has gone close in the past two majors and joined Bradley on two under.
New Zealander Ryan Fox – the son of All Blacks rugby union legend Grant – has battled pneumonia and suffered sleepless nights following the birth of his second child in recent weeks but he too posted a 68.
But only 19 players ended the day under par.
England’s Callum Tarren, who briefly led after a run of three successive birdies from the second hole, closed with bogeys on his final two holes to post a 71.
Compatriot Tyrrell Hatton, fancied by many to go well this week, opened with a 77, while Scotland’s Robert MacIntyre fared a shot better.