Two-time winner Brooks Koepka recovered from playing his first hole like "an idiot" as playing partner Rory McIlroy suffered another slow start on the opening day of the 103rd US PGA Championship.
Koepka hit back from making a double bogey on the 10th to card a three-under-par 69 and lie two shots off the lead held by Canada's Corey Conners at Kiawah Island.
England's Sam Horsfield, 2011 champion Keegan Bradley and Norway's Viktor Hovland were among those alongside Koepka in second place, with five-time major winner Phil Mickelson and Scotland's Martin Laird part of the group on two under.
McIlroy ended the day eight shots off the lead following a 75 which continued his costly habit of bad starts in the game's biggest events.
Since 2015 the 32-year-old is a combined 35 over par in the first round of major championships and again faces an uphill task to win a fifth major title and first since the 2014 US PGA.
McIlroy had come into the event as the tournament favourite on the back of his eight-shot win at Kiawah in 2012 and victory in his previous start on the PGA Tour, but got his campaign under way by carving his tee shot into the water on the par-four 10th.
The resulting bogey was followed by birdies on the 11th and 12th, but McIlroy managed just one more birdie against five bogeys and crucially played the par fives in two over par.
Koepka, who had failed to get out of a bunker at the first attempt on the 10th while McIlroy was deciding where to take his penalty drop, repaired the damage with birdies on the 11th and 13th and also picked up three shots in the space of four holes from the fourth.
The 31-year-old won the US PGA in 2018 and 2019 but had played just four competitive rounds since the end of February after undergoing surgery on March 16 to deal with a knee cap dislocation and ligament damage.
"It's a major. I'm going to show up," Koepka said. "I'm ready to play. I've been itching to do this since Augusta. I mean, I feel so much better now. I don't need to be 100 per cent to be able to play good."
Asked what he was thinking after the double bogey, Koepka added: "What an idiot I was.
"The first rule is, if you're in trouble, get the hell out. I couldn't reach the green. It was a bad lie. Just tried to hit a pull sand wedge up by the green instead of just chopping it out. So mental mistake there. Deserved every bit of that double bogey.
"It kind of helped me refocus. I can't play with any mistakes, maybe one a day, and that was my one, and I got it out of the way the first hole."
The longest course in major history had dominated the build-up to the season's second major, with the Pete Dye-designed Ocean Course on South Carolina's Atlantic coast capable of playing to a maximum of 7,876 yards.
And although it was playing to 'only' 7,660 yards on Thursday, the length and windy conditions were proving a tough test for the world's best players.
Laird had threatened to claim the clubhouse lead with four birdies in a row from the 13th taking him to four under, but bogeyed the 17th and 18th to return a 70.
The English trio of Paul Casey, Tyrrell Hatton and Tom Lewis all shot rounds of 71, while US Open champion Bryson DeChambeau had five birdies and five bogeys in an eventful 72.
World number one Dustin Johnson double-bogeyed the 18th in a disappointing 76, with Open champion Shane Lowry bouncing back from a double bogey on 17 to birdie the last and return a 73 matched by Jordan Spieth.
Before play had got under way, former Open champion Francesco Molinari had been forced to withdraw with a back injury in another blow to his chances of making Europe's Ryder Cup team for September's contest at Whistling Straits.
The Italian became the first European player to compile a perfect 5-0 record in Paris in 2018, but has slipped to 144th in the world and is currently 42nd in the qualifying race.
