LOS ANGELES • World No. 1 Dustin Johnson sent his rivals a warning by powering to an eight-shot win, the biggest margin of his career, at the PGA Tour's Tournament of Champions and insisting he has a lot of room for improvement.

His masterful display off the tee at the par-73 Plantation Course in Kapalua, Hawaii, on Sunday included a near hole-in-one at the 433-yard, par-four 12th hole that came just inches short.

The American golfer, seemingly unaffected by the wind and intermittent rain throughout the round, hit an eight-under 65 for 24-under 268 and his 17th Tour triumph.

"I've really been driving the ball (well) this week," said the 33-year-old, who has a new driver in his bag at the elite 34-man event for last year's tournament winners. "I knew as long as I could keep doing that I was going to play well."

Spain's Jon Rahm was second after a 69 for 276 and is set to rise from No. 4 to No. 3 in the world.

Brian Harman closed with a 72 for third on 277 after starting the day two shots behind Johnson.

The leader put himself out of reach with four birdies on the front nine. His only miscue came at the par-three 11th, where he was in a bunker off the tee en route to a bogey. He rebounded strongly with the monster drive at the 12th and padded his lead with three straight birdies at Nos. 14, 15 and 16.

The win was especially satisfying after his collapse at the HSBC Champions in Shanghai in October, when he led by six after three rounds but closed with a 77 to finish tied for second behind Justin Rose.

Said Johnson: "Even when I made the turn, I think I was 20 under. I told myself to get it to 25. I kind of just kept the pedal down."

And there will also be no let-up when it comes to upping his game.

He said: "I still got a lot of work to do. I feel like I can still improve a lot throughout the bag, and the iron game wasn't as sharp as I would have liked it to be.

"But everything's going in the right direction."

AGENCE FRANCE-PRESSE