JEJU ISLAND, South Korea -- Justin Thomas shot a 9-under 63 on Friday to take a two-stroke lead at the CJ Cup at Nine Bridges, putting himself in position to win his second PGA Tour event in South Korea in three years.
Thomas, who won the inaugural CJ Cup in 2017, has a two-round total of 13-under 131.
South Korean-born New Zealander Danny Lee (66) is in a tie for second place with first-round leader and former U.S. Amateur champion Byeong-Hun An, who shot 69 before his home fans.
Jordan Spieth (65) and Emiliano Grillo (66) are tied for fourth, four strokes behind.
Thomas birdied his first four holes and was 6-under after 10 holes.
"Overall one of the better rounds in a while," Thomas said. "It came pretty easy, for the most part. I never had to worry much out there."
Lee said he had a "positive round."
"It got windy at the end, the last five holes, but my ball-striking has been really nice, and I made some putts," Lee said. "Unfortunately I bogeyed the last hole."
After a 66 on Thursday, Jason Day bogeyed four of his last six holes Friday for a 73 and is eight strokes behind.
Last year's runner-up, Gary Woodland, had a second straight 71 and is 11 behind at 2-under with Phil Mickelson, who shot 72. Defending champion Brooks Koepka had four bogeys on his first nine for a 75 and is 13 strokes behind.
Mickelson had the shot of the day, hitting a 353-yard tee shot that hit the flag on the par-4 14th, stopping 8 inches from the cup. That set up a tap-in eagle.
There are 78 players in the no-cut, limited-field event. It's the first of three PGA Tour events in Asia, continuing next week at the Zozo Championship in Japan that includes Tiger Woods and ending with the World Golf Championship event in Shanghai.