"Not winning makes you want to win more, as weird as that is.
"The top feels far away, and I feel like I have a lot of work to do."
Coming off titles at the Zurich Open and Wells Fargo, McIlroy carried the momentum onto the first tee.
He rolled in a six-footer for a birdie on his opening hole, the par five 10th, then picked up a second at the 13th to briefly join a crowd at the top of the leaderboard.
But the Northern Irishman, who announced on Monday he had filed for divorce, stalled after the early burst.
He took a bogey at the 17th before hitting his stride again after the turn by carding four birdies, including three straight from the fifth.
"Not a pretty 66," summed up McIlroy, who won the last of his four majors in 2014 on the same Valhalla layout.
"I sort of felt like it was pretty scrappy for the most part.
"I thought I got a lot out of my game today.
Sizzling Schauffele grabs first round lead at PGA Championship
Image: Patrick Smith/Getty Images
A rampaging Xander Schauffele powered to the top of the PGA Championship leaderboard on Thursday, firing a record-equaling opening round nine-under 62 at Valhalla Golf Club as the Olympic champion looked to atone for a shock loss at the Wells Fargo.
Out with the early starters, Schauffele set the target no one in the 156-player field could match.
Tony Finau and Sahith Theegala came the closest, returning six-under 65s to sit three back.
Not even the two hottest golfers on the planet, world number one Scottie Scheffler and number two Rory McIlroy, could muster a challenge on a day of ideal scoring conditions at the defenceless Valhalla Golf Club.
McIlroy, coming off back-to-back PGA Tour wins, turned in a scrappy five-under 66 to settle in four off the pace.
Tiger Woods says body ‘OK’ ahead of his third PGA at Valhalla
New father Scheffler, with four victories in his last five starts including a second Masters Green Jacket, lurks one further adrift after returning a 67.
Schauffele, who held a final round two-stroke lead at Quail Hollow on Sunday before losing by five shots to McIlroy, was a man on a mission in Louisville, matching the men's major championship low score for a second time.
Despite an Olympic gold medal in Tokyo and a proven ability to go low, the 30-year-old American has yet to win a major and is without a win since the 2022 Scottish Open.
While there is a lot of golf to be played, the world number three signaled he plans to end both droughts with a brilliant error-free opening round that matched his first round effort at last year's US Open.
Only two other men have returned 62s at a major, Rickie Fowler, also in the first round at the 2023 US Open, and Branden Grace, in the third round at the 2017 Open Championship at Royal Birkdale.
"I'll take a 62 in any major any day," said Schauffele.
"Not winning makes you want to win more, as weird as that is.
"The top feels far away, and I feel like I have a lot of work to do."
Coming off titles at the Zurich Open and Wells Fargo, McIlroy carried the momentum onto the first tee.
He rolled in a six-footer for a birdie on his opening hole, the par five 10th, then picked up a second at the 13th to briefly join a crowd at the top of the leaderboard.
But the Northern Irishman, who announced on Monday he had filed for divorce, stalled after the early burst.
He took a bogey at the 17th before hitting his stride again after the turn by carding four birdies, including three straight from the fifth.
"Not a pretty 66," summed up McIlroy, who won the last of his four majors in 2014 on the same Valhalla layout.
"I sort of felt like it was pretty scrappy for the most part.
"I thought I got a lot out of my game today.
"Not really happy with how I played but at least happy with the score."
After taking three weeks off to be with his wife, who was about to give birth, there were worries Scheffler would need time to shake off competitive rust before returning to his dominating ways.
He wasted no time dispelling those concerns, holing out from 167-yards on the par four first for an eagle and adding a birdie at the fourth to get to three-under.
However, the 27-year-old American could not sustain that level, mixing three birdies with a pair of bogeys over the next 14 holes.
Defending champion and LIV Golf standard-bearer Brooks Koepka, bidding to become the tournament's first repeat winner since he retained the title in 2019, looked a threat to add a fourth Wanamaker trophy to his collection after returning a 67 highlighted by an eagle, birdie and par finish to join Scheffler in a group at four-under.
Tiger Woods, who collected one of his 15 major titles at Valhalla in 2000 with a playoff win over Bob May, opened with a one-over 72 but lamented a sloppy bogey finish to his day.
This is Woods' first event since the Masters. Last month the injury-ravaged golfer earned a tournament record 24th consecutive made cut at Augusta National, though finishing last among those who played the weekend.
"It's just that I don't play a whole lot of competitive rounds," said Woods.
"I haven't played since the Masters.
"So it's a little bit different than being at home and playing a flat Florida course."
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