LOS ANGELES (AFP) - World No. 1 Dustin Johnson says he is taking nothing for granted as he attempts to extend his dazzling run of form at the US PGA Tour's Genesis Invitational at Riviera in Los Angeles on Thursday (Feb 18).

The 36-year-old has been on a roll with five victories in the past eight months, a purple patch that includes wins in the Masters and PGA Tour Championship and five other top 10 finishes.

Johnson's latest title came in the European Tour's Saudi International in Riyadh two weeks ago, where he topped a strong field to win by two strokes.

It has left Johnson in a buoyant mood as he returns to Riviera, where he triumphed in 2017 and has posted eight other top-10 finishes.

But despite the apparently effortless nature of some of his recent displays, Johnson said Wednesday he is still driven by a desire to improve.

"This game is never easy," Johnson said. "Every day something is different.

"Obviously I'm playing well, I've got a lot of confidence in everything that I'm doing. It might be easier, but it's not easy. I've just been playing really consistent and solid golf."

Johnson had an early look at the Riviera layout on Wednesday with a dawn start in the Pro-Am competition. The two-time major champion pinpointed his putting as an area for improvement following the round.

"I feel like I could always be better with every part of the game, but definitely can roll the putter better always," Johnson said.

"I feel like the short game, you can always improve with that, too. But I feel like I'm swinging it pretty good, I'm happy with the way I'm swinging it, but there's room for improvement I think throughout the bag."

Although tournament host Tiger Woods is a notable absentee this week as he recovers from surgery on his sore back, Johnson heads a powerful field that features eight of the world's top 10.

Australia's Adam Scott returns to defend his title while Brooks Koepka aims to maintain the form that saw him storm to victory at the Waste Management Phoenix Open in Arizona earlier this month.

"This is a big tournament, it always is," Johnson said.

"It's always got a great field, it's at a great venue. There's golf courses that I always look forward to going to and playing, and this is one of my favourite courses."

"It's a tough golf course. You've got to drive it well, you've got to be really spot on with your irons and distance control, shot shapes into the green.

"I think it kind of makes you think on every shot you're hitting off the tee."

Johnson meanwhile says that he is not yet thinking about the Masters at Augusta in April, where he will attempt to defend his title after winning last year's rescheduled tournament in November.

"I've got a lot of big tournaments before we get to the Masters," Johnson said.