Brooks Koepka carded a flawless five-under-par 67 to claim a commanding four-shot advantage after the penultimate round of the CJ Cup at Jeju Island in South Korea.

The three-time major winner was able to negotiate a tricky few opening holes before kickstarting his third round with back-to-back birdies around the turn.

He collected further gains at the 14th, 17th and 18th to move to 13 under overall ahead of the final 18 holes, with Ian Poulter and halfway leader Scott Piercy his closest challengers.

Koepka will have his sights set on a fifth PGA Tour title on Sunday - and, remarkably, his first in a non-major since February 2015 when he triumphed at the Phoenix Open.

Ryder Cup star Poulter has an outside chance of clinching his second title of the year after birdies at three of his final four holes.

Poulter, who triumphed in Houston in April after defeating Beau Hossler in a play-off, bounced back from his only bogey on the fourth hole with a birdie on the ninth.

He thrived on the back nine thanks to further birdies on the 12th, 15th, 16th and 18th which helped him card a four-under 68.

Piercy sits alongside the Englishman after an eventful level-par 72, in which he followed up five birdies with as many bogeys.

Spain's Rafa Cabrera Bello is among six players who sit on eight under, while former world number one Jason Day lies a shot further back.

Paul Casey will have his sights set on at least a top-10 finish after shooting up the leaderboard with a six-under 66 on Saturday. 

Graeme McDowell is on four under par after a round of 69.