Gary Woodland holed five birdies on the back nine to surge into the first-round lead of the US PGA Championship.
The American, who has never finished inside the top 10 at a major, carded a six-under 64 at Bellerive, Missouri.
Rickie Fowler began his latest bid to win a first major with a five-under 65, one clear of South Africa's Brandon Stone and fellow American Zach Johnson.
England's Ian Poulter and Justin Rose, plus world number one Dustin Johnson, are in a large group on three under.
Defending champion Justin Thomas ended one under, while playing partners Rory McIlroy and Tiger Woods finished level.
A total of 47 players in the 156-strong field ended the opening day under par at the course on the outskirts of St Louis.
Woodland, ranked 44th in the world, took advantage of favourable conditions - warm, with little wind - late in the day to snatch the overnight lead from Fowler.
The 34-year-old began with a bogey on the first before birdies on the eighth and ninth moved him under par at the turn.
Five more birdies followed on the back half, going into the outright lead with a short birdie putt on the 17th.
It almost got even better with another chance on the 18th - which would have levelled the lowest round at the PGA Championship - only to see his 17-foot effort stop agonisingly short.
"I hit bad shots on one and two, feeling the pressure early. But I really settled in and played great outside of that," said Woodland, who is a native of nearby Kansas and is being supported by a large contingent of friends and family.
"It was nice to get the jitters off early and get rolling. I saw some putts go in."
Fowler has had nine top-five finishes at major championships
Fowler, 29, has long been tipped as a major winner but, despite a number of near misses, has not been able to earn a career-defining triumph at the Masters, US Open, The Open Championship or PGA Championship.
The world number nine has twice finished in the top five at each of the majors.
Starting his opening round on the 10th, he holed six birdies to card his joint-lowest round at a major.
His opening birdie on the 14th was cancelled out when he found the sand on the par-three 16th, but he rolled in a 12-foot birdie putt on the par-five 17th to turn at one under.
Fowler, who found 11 of 14 fairways and 16 of 18 greens in regulation, added four more birdies on the front nine to match his 65 at this year's Masters.
No Englishman has won the PGA Championship, which is being played for the 100th time this week, since Jim Barnes won his second in 1919 and it is two of the country's long-established leading players who are heading the chase.
Poulter, 41, almost lost his PGA Tour card last year, but has battled back into the world's top 30 and is now eyeing a place in next month's European Ryder Cup team after a good run of form.
Among the early starters at Bellerive, he moved to the top of the leaderboard with three birdies in his opening six holes and, after a couple of dropped shots, two more late birdies helped move him back to three under.
"I want to make the team, it's no secret it's important to me," said Poulter of his Ryder Cup ambitions.
"I have this week and the FedEx week to try and push myself in and that's what I'm trying to do."
Rose, 38, decided not to play a practice round at Bellerive as he managed a slight back injury and responded with a round containing five birdies as he also carded a 67.
"In some ways you haven't hit a bad shot and you're not influenced by your practice rounds," said the 2013 US Open champion, who finished joint second at last month's Open Championship and could replace Johnson as the world number one this week.
"I felt very clear about how I wanted to play the course, and that worked out."
Fellow Englishman Ross Fisher is two under, alongside Open champion Francesco Molinari and world number seven Jon Rahm - two of the players set to play for Europe against the United States at the Le Golf National in Paris on 28 September.
Tommy Fleetwood, likely to make his Ryder Cup debut, has finished in the top 20 at each of the three previous majors this year and is a shot further back.
Many players wore yellow ribbons during their rounds in tribute to Australian tour player Jarrod Lyle, who has died of cancer aged 36.
Lyle, who played 121 PGA events between 2006 and 2016, overcame acute myeloid leukaemia in 1998 and 2012, before announcing it had returned last year.
He died on Wednesday, after spending his final days with family and friends.
Lyle's fellow Australian Adam Scott and five-time major champion Phil Mickelson were among the many players wearing a yellow ribbon, which is a symbol to raise awareness about cancer.
Jason Day, another Australian player, fought back the tears as he talked about his "good buddy" Lyle after his round.
"It's hard because you sit there and you know him and he's a buddy of yours, and he's not there anymore," said the 2015 PGA Championship winner. "He's never going to come back.
"That's the hardest thing to sort of come by. Now I'm tearing up."
Australian Adam Scott was one of a number of players wearing a yellow ribbon
Fowler wore a duck pin badge on the front of his cap - a reference to the duck cover Lyle used to have on his driver - while also deciding to wear a yellow shirt in honour of Lyle.
"The last few weeks we've all been thinking about Jarrod a lot," he said.
"I was scripted to wear dark blue but immediately changed. Last week I had the pin on the side and today he's front and centre. It's definitely tough.
"Jarrod wouldn't want us out here feeling sorry and feeling bad, he would tell us to go out and have some fun.
"You're trying to go out there and keep living life like he did, but it's unfortunate that he's not here with us."
Rickie Fowler moved his duck pin badge to the front of his cap