Scott's 11-birdie, eight-under-par 65 left Australia's former World No.1 two strokes behind American leader Denny McCarthy, who came tantalisingly close to posting a 59.

After missing the cut at last week's U.S Open, Scott reached nine-under on Thursday and the outright lead before racking up a double-bogey six after dunking his approach into the water on the par-4 17th hole.

He replied with his 11th birdie of the day to be sharing second with Keegan Bradley.

"It's a shame, but it's hard to be disappointed with a 62," the 42-year-old Australian said.

Fellow American and World No.1 Scottie Scheffler is outright fourth after opening with a 63.

McCarthy had nine birdies through 15 holes at TPC River Highlands, a par-70 course.

Finishing his round on the front nine, he had pars at 7 and 8 before he nearly holed-out for eagle at the par-4 9th to hit the magic number.

His approach shot bounced off a small hill next to the green, redirecting his ball straight toward the pin, where it grazed the edge of the hole.

McCarthy sank a 5-foot putt for birdie to wrap up his 60, shooting 30 on both nines.

Scott was also flirting with a 59 before stumbling late.

The PGA Tour still hasn't seen a 59 since Scheffler's second round at the 2020 Northern Trust Open.

McCarthy, 30, has yet to win a PGA Tour event but lost a play-off to Viktor Hovland at the Memorial Tournament earlier this month.

Cam Davis is the next best Australian in equal eighth after starting with a five-under 65.

Min Woo Lee, fresh off his tie for fifth at the U.S Open, is sharing 16th spot at four-under, one shot ahead of Lucas Herbert, who opened with a 67.

Jason Day will do well to avoid a fourth straight missed cut following a disappointing one-over 71.

Day has been struggling since breaking a five-year winless drought at last month's AT&T Byron Nelson Championship in Texas.