Dustin Johnson signalled his intention to remain world No.1 with an opening 66 in the Players Championship at Sawgrass.

Johnson's position at the top of the rankings, which he has held since February last year, is under threat from Justin Thomas, Jon Rahm, Jordan Spieth and Justin Rose.

But the former US Open champion is not about to make life easy for his rivals and carded six birdies in an error-free first round to share the early clubhouse lead with fellow American Webb Simpson.

Rose is just two shots off the lead after a 68, but Thomas could only manage a one-over-par 73 and Spieth fared even worse with a 75 which featured four bogeys, a double bogey and an eagle on the short par-four 12th. Rahm was among the later starters.

"I haven't had the best record here but it's a golf course that I like, I enjoy playing it and I feel like I should play well here," Johnson said after his lowest score and first bogey-free round at Sawgrass in 31 attempts.

"I felt like it was a really solid day, I drove it really well, hit a lot of greens. I wasn't too sharp with the irons but was still on the green and rolled the putter pretty well.

"My expectation is the same for every tournament, I want to play well and put myself in a position to have a chance to win on Sunday."

Asked about the world ranking situation, Johnson added in a post-round interview broadcast on the PGA Tour's Twitter account: "Justin [Thomas] has been pretty close to me for a while.

"Every week I know there's a chance that someone can pass me. I definitely want to stay there, but if someone passes me it's not going to change anything, I'm still going to go back the next week and try to get it back.

"It was a big deal to get there and it's a big deal to stay there. I like being number one so I want to stay there."

Defending champion Si Woo Kim and Venezuela's Jhonattan Vegas were a shot off the lead on five under par, with European No.1 Tommy Fleetwood three under and last year's runner-up Ian Poulter on two under.

Former world No.1 Rory McIlroy was a shot further back after a 71 which included four birdies and three bogeys.