Rory McIlroy and Shane Lowry enjoyed excellent starts at the final major of the year, the PGA Championship at Valhalla.
McIlroy finished his opening round just one shot off the leaders on five under following a birdie on the final hole.
And the three-time major winner could easily have led at the end of the opening day but for three dropped shots midway through his round as he made a double bogey on the tenth and followed it up with another dropped shot on the 11th hole.
The Open champion had reached the turn on three under, following front-nine birdies on the fourth, seventh and ninth holes.
But the Holywood man handed those shots back as he started the back nine dropping back to level par with seven to play.
However, the champion golfer then showed his class, bouncing back with four consecutive birdies from the 12th to 15th, before finishing with a birdie on the 18th.
Lowry sits three shots off the lead after posting a three-under 68, in a round that included five birdies and two bogeys, leaving the Offaly man in a share for 11th place.
A rejuvenated Lee Westwood set the early pace, while Tiger Woods failed to make an impression on the opening day of the 96th US PGA Championship.
All eyes were on Woods after he declared himself pain free and said he was targeting a 15th major title at Valhalla, despite getting in just nine holes of practice after withdrawing from the final round of the WGC-Bridgestone Invitational with a back injury.
But while the former world number one struggled to a three-over-par 74, Westwood compiled a six-under 65 that was matched minutes later by American Kevin Chappell and by Ryan Palmer later in the afternoon.
Padraig Harrington, who played with Woods and Phil Mickelson (two under), started well but four bogeys on the back nine saw him drift to two over par.
Graeme McDowell was left to count the cost of a double-bogey on the 12th as he also finished two over. Darren Clarke had a disappointing opening round and is unlikely to be around at the weekend.
Westwood, who carded a closing 63 at Firestone Country Club on Sunday after missing the cut in his previous four events, looked to have squandered a good start when he covered the back nine in 33 only to run up a double bogey on the first.
However, the 41-year-old bounced back with a birdie on the fourth and rattled in four more in succession from the sixth, ending his round in style by holing from 40 feet on the ninth.
Italian Edoardo Molinari shot five under par alongside Jim Furyk and Henrik Stenson, while Holland's Joost Luiten and England's Ian Poulter boosted their Ryder Cup chances with rounds of 68 and Colin Montgomerie returned a highly respectable 70.
"I wanted to represent the Champions Tour well and 70 is okay to start with," said Montgomerie, who qualified by winning the Senior PGA Championship in May. "I drove the ball well and knew if I did that I could get round."
World number six Matt Kuchar could not say the same thing, the American withdrawing before the start of play with a back injury as the problems mounted for US Ryder Cup captain Tom Watson.
Dustin Johnson has already made himself unavailable for the team due to "personal challenges" while defending US PGA champion Jason Dufner is struggling with two bulging discs in his neck and withdrew midway through his round.
Kuchar, who has already sealed his place on the Ryder Cup team for Gleneagles, was replaced in the draw by first reserve John Huh.
Westwood, whose 65 eclipsed his previous lowest score in the US PGA - an opening 66 at Oak Hill last year - said: "Last week was a big week for me.
"Going into last week I felt like I had turned the corner. I was starting to swing it a lot better but that's no good unless you start converting it into low rounds. The first three rounds were frustrating because I played a lot better than three over.
"Then obviously I got it going the final day, shot 63. I tried to keep it low key in the practice rounds here, just playing nine holes each day, and carry that momentum through to the first round, which I've managed to do."
In contrast Woods was disappointed with his 74, which featured four bogeys and just one birdie, the former world number one chipping in on the 16th.
"It wasn't very good," Woods admitted. "A lot of bad shots and I never got a putt to the hole. I had plenty of looks to turn my round around and then post something even par, even under par. My swing was dialed in on that range out there. Unfortunately, I didn't carry it to the golf course."
Asked about his back, Woods added: "It's a little bit stiff, but that's about it. I'm going to go get treatment and make sure this thing is nice and loose for tomorrow."