American Chez Reavie hit a four-under-par 68 to take a one-shot lead after the opening day of the PGA Tour's CJ Cup as high South Korean winds played havoc with the rounds of the expected contenders on Jeju Island on Thursday.

The world number 64, whose only tour win came a decade ago at the Canadian Open, carded his fifth birdie at the 16th hole to ease to the front of the field and deny former US Masters champion Danny Willett a morale-boosting lead.

Willett, who has endured two years of miserable form since his shock 2016 Augusta triumph, showed signs of a resurgence after brushing aside an early bogey to notch three successive birdies from the fourth.

Two more at the ninth and 12th gave him a clear lead at four-under but the world number 342 lipped out with a straightforward par putt at the 13th and he had to settle for a share of second with local Kim Si-woo after signing for a 69.

Last year's Player's Championship winner Kim dealt well with the conditions after a double bogey start and his six birdies kept him a shot ahead of compatriot An Byeong-hun, who flirted with the lead but finished with a 70 after two late bogeys.

That was enough for a share of fourth place at the $9.5m tournament with six others, including American Scott Piercy who chipped in for an eagle at the par-five third hole.

Brooks Koepka

World number three Brooks Koepka had the best score of the PGA Tour heavyweights with a one-under 71 for a share of 11th but his round was a typical mix of birdies and bogeys, highlighted by a monster putt at the eighth.

Like his fellow American and playing partner Koepka, defending champion Justin Thomas could take top spot in the world rankings with a victory on Sunday but he has some ground to make up after an opening 73.

Last year's Fedex Cup champion's round never really recovered from a calamity at the fourth hole where he four-putted for a double bogey.

Australian Major winners Adam Scott and Jason Day played together, with the latter matching Thomas's 73 and the former managing only a 75 for a share of 54th despite a delightful downhill putt for a birdie at the ninth.

Their compatriot Marc Leishman, who won the CIMB Classic in Malaysia on Sunday, also shot a 75 after struggling with the conditions on the Nine Bridges course.