JEJU, South Korea -- Luke List fired a 5-under 67 to take a one-stroke lead after the second round of the CJ Cup on Friday.
List, who is looking to win on the PGA Tour for the first time, carded five birdies, including one on the par-5 9th, his final hole, to move to 9 under.
"Some positive vibes there," List said. "Anytime you get a bogey-free you are really happy about it. The wind was tricky but I was able to save par a lot and play solid in the back nine."
Thomas took a three-shot lead into the second round, but an opening 3-over-par 39 on the front brought him back to the pack.
The second-round 74 is Thomas' worst score since an 80 in the second round of the British Open.
Jason Day also struggled en route to a 74 to fall back to 24th at 2 under.
Whee Kim (70) was the highest placed of the 16 South Korean players in the field at 6 under overall, tied for sixth with Patrick Reed (72), Chez Reavie (72) and another Australian, Marc Leishman (72).
Seung Yul Noh carded five birdies and closed with an eagle in a bogey-free 65 for the best score of the day, lifting him to even par overall.
Conditions so far have been windy and List said he expects that to be a factor on the weekend.
"If the wind does not blow out here, there will be a lot of birdies," List said. "If the wind does blow, you can kind of be a little bit more strategic and try to make some pars out there."