Brooks Koepka became the world number one golfer after cruising to a four-stroke victory at The CJ Cup at Nine Bridges.

Koepka dethroned fellow American Dustin Johnson atop the world rankings by claiming the championship following an eight-under-par 64 in South Korea on Sunday.

Three-time major champion Koepka had never topped the rankings but that changed at Jeju Island, where he finished 21 under for his third win in 11 starts and fifth PGA Tour title overall.

Koepka came into the final round with a four-shot advantage and he maintained that lead, capping his triumph with an eagle at the 72nd hole – the new number one recording a back-nine 29.

The two-time reigning U.S. Open holder had an eagle, eight birdies and two bogeys to finish clear of countryman Gary Woodland.

Woodland shot a final-round 63 to earn the runners-up cheque, ahead of Ryan Palmer (62) and Rafa Cabrera Bello (65).

Former world number one Jason Day (67) closed out the tournament tied for fifth alongside Scott Piercy (69) at 12 under.

American star Justin Thomas was 16 strokes off the pace following his four-under-par 68.