"It's absolutely amazing. It's a dream come true," Koepka said during his victory ceremony. "I don't think I ever thought in my wildest dreams I'd be the best golfer in the world. I can't even put it into words."

The tournament, the only PGA event held in South Korea, opened in chilly and blustery conditions on Thursday. And no one benefitted more from the milder and more benign conditions that followed over the next three rounds than Koepka, who shot 65-67-64 in his final three rounds.

When the new rankings are officially announced Monday, Koepka will jump from No. 3 to No. 1 and dethrone compatriot Dustin Johnson, who didn't play at the CJ Cup. No. 2 Justin Rose was also absent.

Koepka entered the final round with a four-stroke lead over the field. And the victory was far closer than the final score indicated. Koepka was nursing a one-stroke lead over Gary Woodland at 18-under when he was preparing for a third shot from the rough off the green at the par-4 16th.

Just when it appeared he'd be lucky to save par, Koepka hit a crisp chip shot and rolled it in for an improbable birdie, which took him to 19-under.

Moments later, Woodland, playing two groups ahead, bogeyed the par-3 17th to fall to 16-under.

Koepka capped off his title with an eagle at the 18th.

Koepka, who began his professional career in Europe, has now won in seven countries -- the US, Spain, Turkey, Italy, Scotland, Japan and South Korea.

He saw his four-shot lead cut in half over the first two holes.

Ian Poulter birdied the opening hole to move to 10-under, and Koepka, after settling for par at the first, committed a bogey on the second hole to drop to 12-under.

Koepka picked up a shot at the par-5 third, where he reached the green in two and had two putts for a birdie. Poulter could only manage par there after missing the green to right with his second shot.

But a two-shot swing at the fourth hole -- Koepka's bogey combined with Poulter's birdie -- cut Koepka's lead to just one.

Woodland was also making a charge, as birdies at the third and the fourth took him to 10-under. Woodland picked up another birdie at the sixth.

Koepka bounced back by making a short birdie putt at the fifth and reclaimed a two-stroke lead over the field at 13-under.

With Poulter starting to fade away, Woodland was within one of Koepka after a birdie at the seventh -- his fourth of the day -- got him to 12-under.

Koepka got his second straight birdie at the sixth for a bit more breathing room at 14-under.

Woodland wasn't going anywhere, and another birdie at the eighth brought him back to within one of Koepka at 13-under.

Woodland then pulled into a tie with Koepka at 14-under following his fourth consecutive birdie at the ninth.

And the back nine was the two-horse race between two of the PGA Tour's longest hitters.

Woodland had his first hiccup at the 10th, where he missed the green to right en route to a bogey that dropped him to 13-under.

Koepka regained a two-shot lead with a birdie at the 10th, and Woodland cut it to one again by making a birdie at the 12th.

Woodland drained a lengthy putt from just off the green at the 13th to tie Koepka at 15-under.

But Koepka later matched Woodland's birdies at the 12th and 13th to hold on to a two-shot lead at 17-under.

Woodland had another birdie at the 15th to get back to within one and birdied the 16th to draw level with Koepka at 17-under.

Koepka continued to answer the bell, draining a 20-footer for birdie at the 15th to retake the lead at 18-under.

And it set the stage for the knockout punch at the 16th. Koepka drove into a bunker at the par-4 hole and his second shot landed in the rough off the green.

The possibility of disaster loomed, but Koepka calmly punched it out and saw the ball roll into the cup.

Koepka said he had a great lie in the rough with the ball sitting up, but he wasn't sure if the ball would go in.

"For that to drop, I definitely felt like I won the tournament right then and there," Koepka said. "I just hung in there. I'm not somebody that's going to panic if things go the wrong way. Pretty sure everybody can tell that. I know I'm going to have some good looks, and when I do, you've got to capitalize on them."

The usually stoic one flashed a wide grin and pumped his fist in celebration. And after Woodland's bogey at the 17th opened up a three-shot lead, Koepka's closing eagle at the 18th almost seemed anti-climactic. (Yonhap)