Lee Westwood equalled his lowest round in a Major with an opening 65 at Valhalla to share the lead with American pair Kevin Chappell and Ryan Palmer at the US PGA Championship.
But Open Champion Rory McIlroy, seeking his third win in succession, was ominously placed just a shot behind alongside fellow Europeans Henrik Stenson, Edoardo Molinari and Chris Wood, as well as former US Open Champion Jim Furyk.
World Number One McIlroy ran up a double-bogey seven on the tenth after hooking his second shot out of bounds and then three-putted the 11th, but responded with four birdies in succession and another on the 18th.
"I was really annoyed," McIlroy said. "The second shot on ten was actually a bit of a shock, it's the worst shot I have hit the last few weeks.
"It came out of the blue and knocked me off track but to come back the way I did was great. I really needed that. It could have been a couple better but if those last few putts had dropped but 66 is a solid start."
Finland's Mikko Ilonen was two shots off the lead after a 67, with Ryder Cup hopefuls Ian Poulter, Joost Luiten and Shane Lowry all another shot back, no doubt much to the delight of watching European captain Paul McGinley.
In contrast, McGinley's opposite number Tom Watson saw Tiger Woods struggle to an opening 74, while Matt Kuchar - who has already secured his place on the team for Gleneagles - withdrew before play began with a back injury and defending champion Jason Dufner pulled out with neck problems after ten holes.
Westwood had made early exits from four successive events before taking advantage of last week's WGC-Bridgestone Invitational not having a halfway cut with a closing 63.
And he carried on where he left off in Louisville with a round containing nine birdies, five of them coming in the last six holes, after a double bogey on the first when his drive finished in a divot on the fairway.
Westwood, whose previous lowest score in the US PGA was his opening 66 at Oak Hill last year, said: "Last week was a big week for me.
"I felt like I had turned the corner and 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."
Westwood had lost a bet with Chappell in a practice round earlier this week but the pair will now be hoping to continue the trend which has seen all three Major winners in 2014 - Bubba Watson, Martin Kaymer and Rory McIlroy - be in the top two after the opening round.
World Number 107 Chappell has yet to win on the US PGA Tour and has recorded just one top-ten this season, while Westwood has a record eight top-three finishes in 66 Major Championships without winning one.
Race to Dubai winner Stenson fired six birdies as he seeks to become the first Scandinavian Major winner, with his only dropped shot of the day coming after he found water at the 15th.
“I was the most pleased with my putting today,” said Stenson.
“I think I played a nice, strategic round out there. I hit some good tee shots and some nice iron shots as well. It was more than anything my performance on the greens that made this round, I would say.
“It's nice to get a good start and shoot a good number on the first day. You can never win anything, but you can play your way out of the tournament.”
Molinari was part of Europe’s victorious Ryder Cup team in 2010, but the Italian has since been blighted by injuries.
However, a runner-up finish in Ireland and a tie for seventh at The Open Championship signalled a return to form which continued with seven birdies and two bogeys.
“It was very good,” he said. “My putter was working nicely. I hit a lot of good iron shots, and off the tee I was struggling a little, but the course luckily was fairly generous, so I didn't do any damage.”