Johnson carded his lowest score - and first bogey-free round - at Sawgrass in 31 attempts, while closest rival and compatriot Thomas finished the day at one over par. Si Woo Kim, who a year ago at 21 became the youngest victor in the championship's 44-year history, was a shot off the lead. Thomas is tied for 86th after one round of play, shooting a 1-over par 73 in the first round. In his previous nine starts, his best finish was a tie for 12th a year ago.
Starting on the back nine, Johnson sank five birdies in the space of seven holes and then moved to six under with another birdie on the second, before making pars for the rest of the round. "The greens were receptive, they're rolling flawless". Mitchell played nine holes of practice on Tuesday and Wednesday, and made his debut with four straight birdies at the start.
"It was definitely a big deal to get there and it's a big deal to stay there".
Simpson, who has four top-10s against just one missed cut this season, briefly held the clubhouse lead after his 66.
"But I liked where the pin was today, there's a really tough slope that's about six, eight feet to the right of the pin that makes chipping to that pin incredibly hard and very inviting for a wedge shot".
"I've learned that you've got to be really smart", Simpson told the Golf Channel about playing TPC Sawgrass.
Johnson has been frustrated by his putting all year, and he made a decision to try "AimPoint", a method some players use to help them read the greens. So they give you opportunities, but I've gotten into trouble in the past when I've gotten too aggressive, tried to make too many birdies and forced things. You can quickly make a big number.
"And I knew that I could put the wedge in there just a little bit to the right of the pin and let it spin down". He was at 7 under in the morning until a pair of bogeys late in his round dropped him to a 67. "I've been playing well lately", Mitchell said.
"It's going to be punishment one of these days for sure". I'll take a look and see how the that group gets on this afternoon and see what that's like, but it was nice. "It will be challenging for sure, I'm well aware of that". All that ruined his day was a double bogey at the par-3 third hole, his 12th of the day. Major champions Justin Rose and Bubba Watson highlighted a group at 68. "I'm very pleased with the way I putted today".
"I think he's done a great job because I feel it's harder to stay there than it is to get there, " said McIlroy, a former No. 1. "Took me a few years to learn that you didn't have to overpower it, not that I can overpower it anymore".
The only problem there is that Johnson, for all his ability, has never finished better than 12th at The Players.
None was anywhere near the lead at The Players Championship.
Mickelson flamed out Thursday with an opening-round 79, and Fowler was on his way to a weekend tee time before he lost a ball in a tree on his 15th hole for a double-bogey.
Four players have a chance to surpass Johnson for No. 1 this week.
Spain's Rahm is four under, while American three-time major victor Spieth struggled to a three-over 75. World No. 2 Thomas, No. 3 Rahm and No. 5 Rose all have a chance to rise to No. 1 for the first time in their careers.
"I definitely want to stay there, but if someone passes me it's not going to change anything", Johnson said.
"I think this should be a major, I really do", Spieth said.
Of note, five of the leading six, and with the exception of Kuchar, began their first rounds from the 10th tee. Casey's withdrawal left 49 of the top 50 players in the field, meaning the 2016 U.S. Open is still the most recent tournament to feature the full top 50.