Fourth-ranked Schauffele, last year's Wells Fargo runner-up, started on the back nine and closed with an eagle at the par-5 seventh, a fortunate par at eight and a birdie at nine to fire a seven-under-par 64 at Quail Hollow in Charlotte, North Carolina.

World number two Rory McIlroy, a four-time major winner, sank a 50-foot eagle putt at the par-5 seventh hole and shared second with Sweden's Alex Noren and two-time major winner Collin Morikawa of the United States on 67.

McIlroy is a three-time champion at Quail Hollow, having taken his first PGA title on the layout in 2010 and added crowns in 2015 and 2021.

Schauffele seeks his eighth career PGA Tour triumph but the first for the 30-year-old American since the 2022 Scottish Open.

Heavy rain delayed the start by an hour for the field of 69 in the last major tune-up for next week's PGA Championship at Valhalla.

The saturated course made things odd for Schauffele from the start.

"It was a weird day as a whole," Schauffele said. "We had a delay. The course was soaking wet. I was able to sort of get into some rhythm kind of quickly which was really nice."

Reigning Olympic champion Schauffele began on the back nine and birdied five of the first eight holes.

The run included putts from just over 17 feet at the 12th and 16 feet at the par-3 eighth plus three others under six feet, although he made his lone bogey off a tee shot way right into the dirt at 18.

Schauffele dropped in a five-foot eagle putt at the par-5 seventh to grab the lead and closed with a six-foot birdie putt at the ninth, but it was the par between them at eight that felt most special.

Schauffele smacked his tee shot well right, deep into trees and rocks, but after finding the ball got relief from a Shotlink tower and two club lengths allowed him to drop into rough.

"The tower was just in the luckiest spot possible," Schauffele said. "The club length got me on the very edge of the pine straw. Hit what I thought was an unbelievable pitch to get it up onto the green. Then it was a no-sweat two-putt.

"A really bad drive after two super shots. I was really lucky one that they found it and two to get that kind of relief out of the absolute dead zone."

"A pretty stressful moment turned into a pretty stress-less par," he said, calling the closing birdie "just a cherry on top."

McIlroy hitting it well

McIlroy, coming off a PGA pairs victory alongside Ireland's Shane Lowry two weeks ago at New Orleans, was pleased at his start.

"It was good to play a solid round," he said. "Left a couple out there, but at the same time I've got three more days to try to build on what I've done.

"I'm hitting the ball really well again, with some of the shots that I hit out there today with the driver, some of the iron shots were much better. I feel like putting is good."

McIlroy reeled off three consecutive birdies from the third to fifth holes, the last a hole-out from just inside 29 feet, before his eagle at seven to seize the solo lead.

But the 35-year-old from Northern Ireland stumbled with a lip-out on a six-foot par putt at the ninth and a birdie-bogey start to the back nine.

McIlroy sank a six-foot birdie putt at the par-3 13th, but made bogey at the par-5 15th after finding two bunkers and the right rough.

He responded with a birdie putt at 16 from just outside eight feet but went left off the 18th tee and missed a seven-foot par putt.