Justin Thomas made a blistering start to The CJ Cup at Nine Bridges, firing a nine-under 63 to earn a three-shot lead on Thursday.
Thomas, the FedEx Cup and US PGA Championship winner this year, was in fine form in the first round in Jeju, South Korea.
The American bogeyed his first hole - the 10th - but was then red-hot, making eagles at 12 and 18 and four straight birdies from 14 through 17.
Thomas slowed on his second nine, but he finished with a 63 after capitalising on the par-fives at Nine Bridges Golf Club with two eagles and two birdies.
The 24-year-old, who was tied for 17th at the CIMB Classic last week, is three shots clear of the chasing pack.
"It was kind of a weird day," Thomas told the Golf Channel. "It started off with a really, really bad bogey and I had a seven-hole stretch there where I basically kind of went unconscious and that was pretty much most of my round."
Patrick Reed birdied his final hole to move to six under, while Marc Leishman is alongside the American after an eagle at the 18th.
Chez Reavie, Gavin Green and Scott Brown also opened with 66s.
In the first PGA Tour event to be played in South Korea, a group of five players are a further shot back in a share of seventh.
Tony Finau, Charles Howell III, Russell Henley, Jhonattan Vegas and Ollie Schniederjans carded 67s.
World number nine Jason Day finished strongly, with birdies on four of his final seven holes seeing him shoot a four-under 68 to be tied for 12th.
His fellow Australian Adam Scott and England's Paul Casey are further back after even-par 72s.