The US Open champion needed to win the tournament and see Day finish worse than a tie for third to claim the No.1 ranking for the first time in his career. He won in a canter while Day, who held the top spot for 47 consecutive weeks, finished in a tie for 64th.

"It sounds good," said Johnson of his elevation to World No.1. "I played really great all day. I couldn't have driven it any better. That was a big key.

"It gives me a lot of confidence. It’s going to push me to work even harder and try to get even better.”

It was a dominating performance from Johnson over a field top heavy with superstars.

RIGHT: Dustin Johnson celebrates his win and move to World No.1 with son, Tatum, and fiancee Paulina Gretzky. PHOTO: Harry How/Getty Images. 

With rain disrupting play in the second and third rounds, Johnson finished his third round on Sunday morning (LA time) with a trio of birdies to sign for a seven under 64, which gave him a five-stroke lead over the field.

He continued to plunder the Riviera course in the final round, stretching his lead to nine shots at one point after birdies on the 1st, 2nd and 6th holes. His birdie on the par-3 6th was so matter-of-fact – tee shot to 12 feet, hole the putt, move on – that he threatened to demoralise the strong field with a double-digit victory margin. Instead, he took the foot off accelerator and dropped three shots in his last 10 holes (after only making one bogey in the first 62 holes) to card a closing even par 71 and the biggest margin of victory in his career.

"I didn't finish the last 10 holes the way I'd like to, but I had a pretty good lead. I was on cruise control," Johnson said.

Johnson lags his first putt down the hole on the 18th green. PHOTO: Getty Images.

Having tapped in for the win, he walked across the 18th green to be greeted by his two-year-old son, Tatum, and fiancee, Paulina Gretzky. The win caps a great week for the couple who announced a few days ago they are expecting their second child.

Johnson, who will now be the raging hot favourite for the Masters in April, has won every year since joining the Tour in 2008, which is the longest active streak on the PGA Tour

The 32-year-old joins Arnold Palmer, Jack Nicklaus and Tiger Woods in winning every year for at least a decade after starting on the Tour. Palmer and Nicklaus both won their first 17 seasons, while Woods notched 14 straight seasons with a win.

FINAL LEADERBOARD

Belguim’s Thomas Pieters (63) and American Scott Brown (68) finished tied second on 12 under. Pieters was flawless in the final round and his runner-up finish will go a long way to him securing a PGA Tour card by season’s end.

Adam Scott was the best of the Australians, finishing in a tie for 11th having closed with a one under 70.

“I hit it sideways all day and the score kind of flatters the way I hit it,” said Scott, who birdied his final two holes to get under par.

The Queenslander now heads to PGA National in Florida to defend his Honda Classic title.