Jason Day has crashed late in the second round of the PGA Tour's CJ Cup in South Korea, but American Justin Thomas has scorched the Nine Bridges course with a nine-under-par 63 for a two-stroke lead.
After an opening-round 66 for outright third, Day bogeyed four of his last six holes on Friday for a 73 to be eight shots behind.
Cameron Smith is the best-placed Australian, firing a three-under 69 to be in a three-way tie for sixth. Smith is eight under overall, five strokes behind Thomas.
Day has slumped to equal 18th, three strokes adrift of Smith.
Marc Leishman is tied 28th, three under after two rounds, after shooting a 69, one ahead of Matt Jones.
Thomas, who won the inaugural CJ Cup in 2017, has a two-round total of 13-under 131.
South Korean-born New Zealander Danny Lee (66) was tied second with first-round leader Byeong Hun An, who shot 69 with his parents in the gallery.
Thomas birdied his first four holes and was six under after 10 holes.
"I didn't do anything unbelievably. It was just was a very stress-free day," Thomas said.
"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. 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."
Jordan Spieth (65) and Emilaino Grillo (66) were tied for fourth, four strokes behind Thomas.
"It's been seven weeks since I've played a tournament round. I'm obviously very pleased," Spieth said.
"I thought the idea was to get some reps on the golf course in tournament play with what I've been working on over the last couple of weeks and, day to day, it felt a little more comfortable.
"I rolled in a lot of putts today, and certainly don't want to have to rely on that over the weekend. That was one of the better putting rounds I can remember having."
Last year's runner-up Gary Woodland had a second-straight 71 and was 11 behind at two under with Phil Mickelson, who shot 72. World No.1 and defending champion Brooks Koepka had four bogeys on his first nine for a 75 and was 13 strokes behind.
Mickelson had the shot of the day a 353-yard tee shot which hit the flag on the par-4 14th, stopping 8 inches from the cup. That set up a tap-in eagle.
There are 78 players in the no-cut, limited-field event. It's the first of three PGA Tour events in Asia, followed by Japan's Zozo Championship featuring Tiger Woods and the WGC event in Shanghai.
Australian Associated Press
