Anthony Kim shot a 6-under 66 on Friday to grab a three-shot lead after the second round of the CJ Invitational.
The American had a bogey on the first hole but made seven birdies the rest of the way for a 10-under total of 134. Tournament host K.J. Choi was tied for second after a 70, along with fellow South Koreans David Oh and Lee Ki-sang.
"I had a few good breaks go my way today but hopefully I won't need them this weekend," Kim said. "I made a couple of key putts and had a good attitude even though I was in the trees a lot. Mentally I'm fresh and physically I'm getting better."
Choi was frustrated with his performance, especially with the three bogeys he recorded on the back nine.
"My scorecard reflects how I played today," Choi said. "It was an up and down day. Sometimes, I hit a shot too well and ran past the green and made bogeys. Made me sick and I lost my rhythm."
Kim said he expected the Choi to recover and make a run at the title this weekend.
"I know he wants to win badly since this is his own tournament," Kim said. "He's a world-class player and he's shown that over the years. I'm expecting him to be up there and I'm going to do my best to chase him."
First-round leader Lee Min-chang only managed a 75 at the Haesley Nine Bridges Golf Club to drop seven shots behind Kim.