Davis Thompson, making his third PGA Tour start as a professional, fired a nine-under par 63 on Thursday to take a two-stroke lead in the Rocket Mortgage Classic in Detroit, Michigan.
Thompson fired nine birdies without a bogey to equal a Detroit Golf Club record and lead England's Tom Lewis, Chile's Joaquin Niemann and American Brandon Hagy by two strokes, but the 22-year-old wasn't getting ahead of himself with three rounds to come.
"Sounds good on Sunday," Thompson said of hearing himself described as tournament leader. "It's only Thursday. I know I've got a long way to go."
Thompson, playing on a sponsor's exemption, missed the cut at the Travelers Championship last week after tying for 35th in his professional debut at the Palmetto Championship in June.
Thompson missed just one green in his bogey-free round, which was disrupted by a rain delay of more than three hours.
"If the putter gets hot, you can just kind of ride that wave throughout the day," said Thompson, who matched the course record shared by Nate Lashley and JT Poston.
"I've played in a few pro events now, so you've just got to keep your emotions in check," he said. "Anything can happen. I know I'm playing well, so I'm just going to have some confidence going into (Friday) and, hopefully, I can play another good round."
Ireland's Seamus Power and American JJ Spaun shared fifth on 66 and Australian Jason Day headed a group of a dozen players on 67.
Defending champion Bryson DeChambeau, who split with caddie Tim Tucker on the eve of the tournament, launched his defence with an even par 72.
After bogeys at the second and third holes DeChambeau rallied with birdies at the fourth, seventh and eighth but made the turn at even par after a bogey at the ninth.
He parred his way in to leave himself work to do to make the cut on Friday.
?? Thompson tops leaderboard
— PGA TOUR (@PGATOUR) July 2, 2021
?? Drivers off the deck in Detroit
?? DeChambeau & Champ drop bombs
All that and more from @RocketClassic in The Takeaway presented by @FedEx. pic.twitter.com/DvJg9Opk8V
Leading first-round scores on Thursday in the US PGA Tour Rocket Mortgage Classic in Detroit, Michigan (USA unless noted, par-72):
63 - Davis Thompson
65 - Brandon Hagy, Tom Lewis (ENG), Joaquin Niemann (CHI)
66 - Seamus Power (IRL), JJ Spaun
67 - Jason Day (AUS), Kevin Kisner, Satoshi Kodaira (JPN), Matthew Wolff, Kim Si-woo (KOR), Fabin Gmez (ARG), Hank Lebioda, Michael Gligic, Troy Merritt, Pat Perez, Robert Streb, Chris Kirk