Justin Thomas shot a stunning nine-under 63 Friday on Jeju Island to take control of the CJ Cup from home favourite An Byoung-hun as world number one Brooks Koepka's title defence evaporated with a 75.
Overnight leader An was reeled in by the relentless Thomas who started four shots behind but finished two in front after setting the South Korea event's 36-hole tournament record on 13-under 131.
"That was, I would say, overall one of the better rounds I've played in a while," Thomas declared after equalling his own best round at the $9.75 million US PGA Tour event.
"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," said Thomas, who also shot 63 in the opening round two years ago on the way to victory.
"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."
- 'Work to do' -
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"Just got to go out tomorrow and hit as many greens as possible and keep rolling it the way I've been rolling it."