Dustin Johnson has taken Jason Day’s world No.1 golf ranking after blitzing the field for a five-shot victory at the Genesis Open at Riviera Country Club.

Johnson, who was third in the world rankings, started his weather-delayed final round at the US PGA Tour event in Los Angeles with a six-shot lead.

Despite three bogeys, Johnson’s even-par round of 71 was enough for a 17-under-par total and a comfortable five-shot triumph over Belgian star Thomas Pieters and Scott Brown.

With Australian Day’s uncharacteristically poor form since returning from a three-month injury hiatus, Johnson needed a victory at Riviera and for Day to finish worse than a three-way tie for third to assume golf’s top spot.

Day – who has held the No.1 ranking for 47 consecutive weeks since March 2016 – handed Johnson the crown with rounds of 70, 70, 75, 71 dropping the 29-year-old to a two-over total and a share of 64th place.

“He deserves it because he’s been playing great golf,” Day said of Johnson, who has finished no worse than third in eight of his last 16 tournaments.

Day is projected to be 0.5 points behind Johnson when the rankings are adjusted, meaning a victory next start at the World Golf Championship event in Mexico in two weeks would likely catapult the Queenslander back to No.1.

“The biggest thing for me is not focus on the rankings. I’ve just got to keep trying to improve each and every week,” Day said.

“You’ve got to focus on winning; if you do that, then it takes care of everything.

If he gets to No.1 again, Day believes he’ll be better equipped to deal with the extra pressure.

“It was tough; a lot of uncomfortable situations you’re just not used to,” he said.

“More pressure, a lot more time commitments but that’s just part and parcel of being (No.1).

“I know exactly what I need to do going into the future and hopefully I can take better steps trying to hold that position once I get back.”

World No.7 Adam Scott – who won at Riviera in 2005 – continued his good record in Los Angeles with birdies on his final two holes to sign for a 70 and finish as the leading Australian at nine under in a tie for 11th.

Scott finished four shots ahead of compatriot Cameron Smith (72), who dropped to a share of 28th with his five under total.

Cameron Percy rounded out the Australian contingent with a final-round of two-over 73 sinking the Victorian to two under sharing 49th.