Justin Thomas defeated Marc Leishman on the second play-off hole to clinch the CJ Cup @ Nine Bridges for his fifth PGA Tour title of a memorable calendar year.

The US PGA Championship winner and Leishman both birdied the final hole in regulation to move to nine under at Jeju Island, edging out Cameron Smith by one shot.

Neither was able to initially repeat the trick as they returned to the 18th to determine a winner, but Leishman found water with his approach second time around and his subsequent bogey opened the door for Thomas.

The American left himself a simple tap-in for birdie to wrap up yet another tour title although it has not been plain sailing for the world number four this week.

He sparkled on the back nine in an opening nine under par 63 although scores of 74 and 70 in his next two rounds opened the door for his rivals while a double-bogey seven on the par-five third left him in trouble in windy conditions on Sunday.

He told the PGA Tour website: "I just kept telling myself it was a bad golf swing, it wasn't a mental error or a wrong judgement that we made, it was just a bad golf swing at a pretty bad time.

"You're going to make bogeys out here and I played the first two holes really well and really played some great golf after that third hole. It's such a long day with these conditions."

Birdies at the ninth, 10th and 11th brought him back into contention although he then made bogeys at the 13th and 17th before ending his round by picking up a shot on the 18th for a level-par 72.

That drew him level with Australia's Leishman, who recorded a two-under 70 in his final round before being edged out in the play-off.

Home hope Whee Kim finished fourth on six under overall while American quintet Pat Perez, Jamie Lovemark, Brian Harman, Luke List and Scott Brown and India's Anirban Lahiri were a shot further back. 

Graeme McDowell finished the tournament on 12 over after a consecutive round of 77.