SEOUL (Reuters) - Justin Thomas made the most of benign conditions to shoot a nine-under 63 on Friday and take a two-stroke lead at the halfway stage of the CJ Cup on the South Korean resort island of Jeju.
The American's blemish-free second round also put him in contention to win the PGA Tour event for the second time in three years having also won the inaugural edition in 2017.
Thomas birdied his first four holes, picked up another shot on the eighth before sinking four more birdies on the back nine at Nine Bridges Golf Club to reach a 13-under 131 total.
Overnight leader and local favorite An Byeong-hun shot 69 to tie for second spot with South Korean-born New Zealander Danny Lee (66) on 11-under.
"I didn't do anything unbelievably, it just was a very stress-free day," Thomas said after his round.
"I think I hit every green and made a couple putts early. And then the back nine, I got a few close to the holes where those birdies came easier.
"So it just was a very easy 63 if you can somehow say that, but hopefully we'll be able to keep some of that going for the weekend."
The 26-year-old rated the 63 he registered two years ago at the tournament as better than Friday's round.
"I'll take 63 on any conditions on any course any day, but it was very, very benign out there," Thomas said. "There just wasn't very much wind, which made it a lot easier to score.
"I felt like when I had control of the ball like I did today, it made it quite a bit easier."
American Jordan Spieth (65) and Emiliano Grillo (66) of Argentina were tied for fourth, four strokes behind Thomas in the first tournament of PGA Tour's three-event Asian swing.
The Tour next heads to Japan for the inaugural Zozo Championship before moving to China for the WGC-HSBC Champions.
Brooks Koepka's title defense appeared to be wilting with the American world number one recording a three-over 75 in the second round and falling 13 strokes behind the leader.
(Reporting by Sudipto Ganguly in Mumbai; editing by Peter Rutherford)