A nine-under-par round of 63 sent Justin Thomas to the top of the leaderboard at The CJ Cup in South Korea.
Thomas, the champion at Nine Bridges two years ago, had nine birdies, including four in the first four holes, and no dropped shots to move to 13 under after two rounds.
That left the American two shots ahead of first-round leader An Byeong-hun, who followed up a 64 with a 69.
“I played well,” former world number one Thomas said. “I didn’t do anything unbelievably. It just was a very stress-free day.
“Obviously playing well, that makes it stress free, but I just kind of kept the ball in play off the tee, hit some good irons.
“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.”
Graeme McDowell followed up his opening round of 68 with a 71 on Friday - he sits on five under par for the tournament and eight strokes off the lead.
Korean-born New Zealander Danny Lee is tied for second with An after a 66. It would have been one better but for a bogey at the par-five 18th.
American Jordan Spieth and Argentina’s Emiliano Grillo are two shots further back in a tie for fourth. Spieth was one of the big movers of the day thanks to a 65.
England’s Tyrell Hatton is in a tie for ninth place on seven under after shooting a 68 while a 73 dropped Australia’s Jason Day from third to a tie for 18th.
Collated second round scores and totals in the USPGA Tour The CJ Cup at Nine Bridges, Nine Bridges, Jeju Island, Korea (USA unless stated, par 72):
131 Justin Thomas 68 63
133 Danny Lee (Nzl) 67 66, Byeong-Hun An (Kor) 64 69
135 Emiliano Grillo (Arg) 69 66, Jordan Spieth 70 65
136 Cameron Smith (Aus) 67 69, Kyoung-hoon Lee (Kor) 69 67, Ryan Moore 69 67, 137 Tyrrell Hatton (Eng) 69 68, Charles Howell III 67 70, Si Woo Kim (Kor) 69 68
138 Wyndham Clark 71 67, Kiradech Aphibarnrat (Tha) 69 69, Jung-Gon Hwang (Kor) 67 71, Joaquin Niemann (Chi) 65 73, Viktor Hovland (Nor) 69 69, Kevin Streelman 69 69
139 Jason Day (Aus) 66 73, Hideki Matsuyama (Jpn) 69 70, Charley Hoffman 67 72, Graeme McDowell (NIrl) 68 71, Ryan Palmer 70 69
140 Kevin Na 72 68, Andrew Putnam 70 70, Rory Sabbatini (Svk) 71 69, Dylan Frittelli (Rsa) 70 70, Soomin Lee (Kor) 68 72
141 Tommy Fleetwood (Eng) 71 70, Marc Leishman (Aus) 72 69, Ian Poulter (Eng) 69 72, Nate Lashley 72 69, Sungjae Im (Kor) 68 73
142 Hyungjoon Lee (Kor) 71 71, Pat Perez 73 69, Harold Varner III 71 71, Matt Jones (Aus) 72 70, Branden Grace (Rsa) 71 71, Gary Woodland 71 71, Sung Hyun Park (Kor) 74 68, Phil Mickelson 70 72, Chase Koepka 70 72, Collin Morikawa 69 73, Kevin Tway 70 72, Rafael Cabrera-Bello (Spa) 68 74, Corey Conners (Can) 70 72
143 Sergio Garcia (Spa) 73 70, Lucas Glover 74 69, Cheng-Tsung Pan (Tai) 74 69, Kyung Ju Choi (Kor) 69 74, Jhonattan Vegas (Ven) 73 70
144 Brooks Koepka 69 75, Sung Kang (Kor) 72 72, Scott Piercy 72 72
145 Luke List 70 75, Joel Dahmen 74 71, Adam Schenk 71 74, Yi-Keun Chang (Kor) 73 72, Adam Long 73 72, Billy Horschel 71 74, Chez Reavie 68 77
146 Vaughn Taylor 74 72, Keith Mitchell 74 72, Troy Merritt 74 72, Jeongwoo Ham (Kor) 74 72
147 Won Joon Lee (Aus) 74 73, J.B. Holmes 70 77, Abraham Ancer (Mex) 73 74, Danny Willett (Eng) 76 71
148 Brian Stuard 72 76, Jazz Janewattananond (Tha) 74 74, Michael Kim 76 72, Kyong-jun Moon (Kor) 76 72
150 Yongjun Bae (Kor) 78 72
151 Matthew Wolff 73 78, Max Homa 69 82, Whee Kim (Kor) 76 75, Tae Hee Lee (Kor) 74 77, Chesson Hadley 75 76
