Australia's Jason Day shot a 5-under-par 65 on Thursday to take a one shot lead after the morning wave of the first round of the PGA Championship in San Francisco.
Day, who parted with long-time swing coach Colin Swatton last week, went bogey-free around the challenging TPC Harding Park.
The former No. 1-ranked player in the world claimed his lone major title at the 2015 PGA Championship and the leaderboard was chock full of former PGA champions.
That includes two-time defending champion Brooks Koepka, who is in a deep group of players at 4-under that also included 2010 champion Martin Kaymer of Germany.
Koepka had admittedly not been playing well while dealing with pain in his left knee. But he tied for second place at last week's WGC-FedEx St. Jude Invitational and the four-time major winner has a reputation for showing up big in marquee events.
"I love the competition," he said. "I love it when it's extremely difficult. Every shot, there's a lot of consequences.
"When you play tough golf courses like this, you've got to really narrow your focus off the tee, put it in the fairway and just go one shot at a time. Just keep plugging away."
Also at 4-under is England's Justin Rose, who managed a 66 despite hitting only three fairways, Bud Cauley, Zach Johnson, Xander Schauffele and Brendan Steele.
Four-time PGA champion Tiger Woods turned in a solid 2-under 68 after making a switch in putters this week. Starting on the back nine in a group with No. 1 Justin Thomas and No. 3 Rory McIlroy, Woods got to 3-under before a bogey on the par-3 eighth hole.
"It was positive," said Woods, who added that the morning wave had the more favorable conditions Thursday. "We were surprised at some of the pin positions, they were a little bit more on the difficult side. This golf course is all about hitting fairways."
Woods felt comfortable while playing with a different version of the Cameron putter he has been using since 1999.
"I've been messing around with this thing for over a year," Woods said. "One of the things that is a lot easier is not to bend over. With my back being the way that it is, and it's fused, it's a little more difficult to bend over."
Thomas and McIlroy, two other former PGA champions, did not fare as well.
McIlroy did rebound from a stretch of three consecutive bogies on his front nine to briefly get back under par. However, he struggled with his distance control on the greens and had to settle for an even-par 70.
Thomas' struggles primarily came off the tee box. That included the newly-minted No. 1 player in the world losing a ball in a cypress tree off the seventh hole, leading to one of two double bogeys in a 1-over 73.
Thomas did close out his round with one of only three birdies on the ninth hole during the morning wave. He is coming off a win at the WGC and has former Phil Mickelson caddie Jim "Bones" Mackay on his bag for the second consecutive week with Jimmie Johnson ill.
NOTES: The PGA Championship is serving as the first major of the year for the first time since 1971, and there are no spectators on the grounds due to the coronavirus pandemic. ... Koepka is aiming to be the first player to win the same major three consecutive times since Peter Thomson at The Open Championship from 1954-56. He is also seeking to become the first player since Woods in 2005-08 to win at least one major in four consecutive seasons. ... Woods is a 15-time major champion and 82-time winner on the PGA Tour, the latter tied with Sam Snead for the most all-time. He won a WGC event at Harding Park in 2005. ... Thomas regained the No. 1 world ranking for the first time since 2018 with his victory last week.
--Field Level Media