American Jim Herman went bogey-free in the opening round of The Honda Classic, carding a five-under-par 65 on Thursday.
Herman - a 2014 Web.com Tour Finals graduate - holed five birdies in a faultless display that saw him move a shot clear at the PGA National Golf Course in Palm Beach Gardens, Florida.
Set up by birdies at the fourth and eighth holes, the 37-year-old added another three after the turn, including at the 18th, to earn an unlikely lead at the PGA Tour event.
Compatriot Brendan Steele is a shot further back following his first-round 66.
"I don't recall ever leading [on the tour]," said Herman, who was ensured of his entry into the field on Monday. "It was a little unexpected to get to five under.
"I was trying to keep it around par, thinking if you could get a birdie here or there and sneak in at one or two under par, it would be great."
All eyes were on world number one Rory McIlroy, who was making his first PGA Tour appearance of the year, but the Northern Irishman endured a forgettable return to the United States as he ended the day three over.
McIlroy had two double-bogeys on the front nine, though he recovered after the turn with back-to-back birdies to end his round.
Irishman Padraig Harrington and American duo Martin Flores and Patrick Reed fared much better.
The trio posted opening rounds of 67 to be two shots behind Herman at three under.
A group of seven players are tied for sixth spot through 18 holes.
Daniel Berger, Scott Piercy, Martin Kaymer, Rory Sabbatini, S.J. Park, David Lingmerth and Jamie Donaldson are level at two under heading into the second day of play.