Australian Lucas Herbert reeled off six straight birdies before a closing par to grab a two-stroke lead early in Thursday's first round of the US PGA Tour's Fortinet Championship.
The 27-year-old Aussie made 10 birdies against a lone bogey to fire a nine-under par 63 at Silverado in Napa, California.
That matched his career-low 18-hole PGA Tour score, which he first managed in last year's final round of the Zozo Championship.
"Found a little groove there," Herbert said. "It felt like anything I did poorly seemed to work out nicely for me and the good shots got rewarded as well.
"Felt like I played OK and just got a lot of good breaks and capitalised on chances as well."
South Korea's Kim Seong-hyeon was second after a bogey-free 65 with much of the field still on the course.
Herbert, whose only US PGA Tour title came at the 2021 Bermuda Championship, is a three-time winner on the DP World Tour, his most recent such crown coming in April when he won the ISPS Handa Championship in Japan with a birdie on the second playoff hole to defeat Canada's Aaron Cockerill.
In all, Herbert had 22 putts that rolled just over 144 feet after taking a seven-week break following a missed cut in July's British Open.
"I felt like coming here I was ready to play again," he said.
After birdies at the third and par-5 fifth holes, Herbert took a bogey at six but answered with a 28-foot birdie putt at the seventh and began the back nine with a 24-foot birdie putt.
His epic birdie run, twice as long as his prior PGA career-best streak, began with tap-ins at the par-5 12th and par-4 13th. He then sank birdie putts from nine feet at 14, just inside five feet at the par-5 15th and 16 feet at 16 and the par-3 17th.
The event launched the PGA's fall season, a series of events after the FedEx Cup playoffs and before the start of the 2024 season that primarily allows players outside the season's top 70 to qualify for spots on next year's tour.
Among the exceptions was two-time defending champion Max Homa, who fired an opening-round 70. The world No 7, who will play on the US Ryder Cup team later this month, seeks his first win since January at Torrey Pines.