US Open champion Wyndham Clark holds a healthy four-shot lead at the midway point of the Players Championship after posting a second-round score of 65, seven under par.
Xander Schauffele and Nick Taylor are at 10 under, with Matt Fitzpatrick and Maverick McNealy a shot further back.
World number one and defending champion Scottie Scheffler battled back from a neck injury to improve to eight under.
Rory McIlroy mixed five birdies with four bogeys and a double bogey as he fell to six under with a 73.
The world number two, who was joint leader overnight with Clark, is eight shots behind the leader despite 15 birdies in his first 36 holes.
McIlroy struggled to match the control he showed Thursday as he raced around the iconic Sawgrass course.
He made three bogeys and three birdies in his first six holes, then another birdie at the ninth was negated by a bogey at the 12th.
Although the Northern Irishman made a 16-foot birdie the next, a wayward drive into the sand led to a double bogey on the 14th.
While he worked hard, Scheffler showed remarkable resilience, making five birdies on his 69 despite playing most of the round in discomfort.
The American, who started on the 10th hole, said: “I hit a shot on my second hole and I felt a little something in my neck.
“Then I tried to hit my tee shot at 12 and that’s when I could barely get the club back. So I had treatment, maybe that’s is a little relaxed, but most of the day I worked hard.
“I’ve done what I can to stay in the tournament and hopefully it will relax and then I can make somewhat normal swings.
“The way I was moving around the course, the way my neck felt, I didn’t know if I was going to be able to continue playing, so yeah, good fight there.”
The 28-year-old, who won the Arnold Palmer Invitational last week by five strokes, is seeking to become the first player to win back-to-back players’ titles in the 50th edition of the PGA Tour’s flagship tournament.
But he will enter the third round Saturday in sixth place behind Clark, who won earlier this season at Pebble Beach.
Clark made five birdies in six holes to pull away from the field and birdied two more in his final four holes to take control of the tournament.
“My iron game has been really solid, I’ve made a handful of putts and then I’ve been really strong mentally, so I would say all those things are why I’m sitting where I am right now “said the American.
Fitzpatrick, the man Clark managed as U.S. Open champion, built on his opening round 66 by taking the lead at 10 under with four birdies in six holes around the turn.
But he hit his second shot into the water on his 13th hole, dropping two shots. A birdie on the par-five ninth, his final hole, saw him sign for a 69.
“Anything can happen over the weekend, so it’s just about trying to stay patient, keep doing what I’m doing and go from there,” said the Sheffield-born player.
Olympic champion Schauffele followed his opening 65 with a 69 that included a double bogey after finding water on the par-five 11th and an eagle three on the long 16th after hitting his second shot to nine feet.
He was joined at 10 under at the end of the day by Canadian Taylor, who birdied the 15th and 16th holes to score a 68.
The infamous 17th claimed yet more victims, with Beau Hossler hitting the 1,000th ball in tournament history into the water that nearly surrounds the par three green.
Englishman Justin Rose also fell into the hole. He was in contention to make the cut when he stood on the tee at one under, but put two balls in the lake as he made a ruinous quadruple bogey seven that sent him to three over par.
Several players will return Saturday to complete their second rounds after darkness once again curtailed play, but the projected cut line of one under means Rose will join American duo Jordan Spieth and Justin Thomas who will miss the final two rounds .