(Reuters) - Dustin Johnson secured the world number one ranking in style when he smoked the field for a five-stroke victory at the Genesis Open in southern California on Sunday.

With the victory, American Johnson jumps from third to first in the world rankings, supplanting Australian Jason Day, who finished tied for 64th.

"I believe in myself. I think I'm a great player," said a delighted Johnson after his runaway victory.

Johnson started the final round with a five-shot lead and was never headed after birdies at the first two holes en route to a closing 71 on the storied Riviera course.

Despite two late bogeys, he finished at 17-under-par 267, with Thomas Pieters (63) of Belgium and American Scott Brown (67) a distant second on 12-under in the event formerly named the Los Angeles Open.

Pieters, a member of last year's European Ryder Cup team, sank a 15-foot birdie at the final hole to give him enough prize money for Special Temporary Membership of the PGA Tour, which means he can accept unlimited tournament invitations.

Former world number one Jordan Spieth, winner last week at Pebble Beach, tied for 22nd, 11 strokes off the pace.

Johnson, 32, collects $1.26 million for his 13th PGA Tour victory. He has won at least once every year since joining the Tour in 2008, the longest active streak.

"It was a long day but played really great all day," Johnson said after a marathon 36-hole Sunday which made up for Friday's near washout when the area was lashed by a strong winter storm.

"To finally get a win (at Riviera) feels good because I’ve finished second here a couple of times, lost in a playoff, felt I should have won a couple of other times."

Johnson effectively put the tournament away when he birdied the final three holes of the third round, and then added two more starting the final round as he threatened the tournament record low score.

"I couldn't have driven it any better," he said. "That was a big key for me today. "I put in a new driver this week. I never was really in any trouble. I made one bogey through 60-something (62) holes."

With victory in sight, however, Johnson started playing conservatively, and three bogeys in the final 10 holes took a little gloss off his performance, but hardly matter in the big picture.

The reigning U.S. Open champion joins Arnold Palmer, Jack Nicklaus and Tiger Woods in winning every year for at least a decade after starting on the tour.

Palmer (1955-71) and Nicklaus (1962-78) both won their first 17 seasons, while Woods (1996-2009) notched 14 straight seasons with a win.

(Reporting by Andrew Both in Cary, North Carolina; Editing by Gene Cherry/Peter Rutherford)