Unheralded Roberto Castro shot a nine-under 63 to tie the course record and grab an early three-shot lead over Rory McIlroy and Zach Johnson in Thursday's opening round of the Players Championship.
Staging a clinic with his irons to receptive greens, Castro, ranked 267th in the world, made seven birdies and an eagle to match the mark shared by Greg Norman and Fred Couples in his first competitive round on the Stadium Course at TPC Sawgrass.
"It gives me proof that when you play great, you're good enough," Castro, 27, said about the confidence boost he gained from his brilliant round.
Castro's playing partner, Jason Bohn, said he had never seen anything quite like the red-haired American's round.
"Ultra impressive," said Bohn, who shot a four-under 68.
"I've never seen a 63 shot like that. His iron play was like a clinic, he had so many kick-ins. That's the highest score he could have shot. He was awesome."
World number two McIlroy also took advantage of greens softened by last week's heavy rains to reverse a trend of poor results for him at Sawgrass, where he had previously never broke par or made the cut in three prior appearances in the tournament.
Tied for fourth place on five-under 67, were Americans Hunter Mahan, Steve Stricker and Casey Wittenberg, with Bohn and Swedes Henrik Stenson and David Lingmerth a further shot back.
World number one Tiger Woods, former Masters champion Bubba Watson and four-times major winner Phil Mickelson were among the late starters.
Castro, whose best PGA Tour finish is a tie for seventh at last year's Greenbrier Classic and whose best result this year is a tie for 16th at Phoenix, gained a jolt of momentum as he finished his opening nine.
Starting on the back nine, he made the turn in five-under 31 with birdies on each of the challenging finishing stretch called "The Gauntlet."
He two-putted the par-five 16th from 65 feet, tapped in at the par-three 17th island green from 19 inches and at the par-four 18th from 23 inches.
Castro eagled the par-five second hole after hitting a three-iron inside four feet to take sole possession of the lead. He followed that with birdies from 21 inches at number four and from 18 inches at the sixth.
"I hit it close a lot," said Castro, whose aunt, Jenny Lidback, played on the LPGA Tour and whose family on his mother's side comes from Peru.
Castro set up his irons with his accuracy off the tee, hitting all but one fairway and 15 of 18 greens in regulation. He had 10 one-putts and 26 putts in all.