US Open champion Wyndham Clark holds a healthy four-shot lead at the halfway point of the Players Championship after carding a second seven-under-par 65.
Xander Schauffele and Nick Taylor are on 10 under, with Matt Fitzpatrick and Maverick McNealy a stroke further back.
World number one and defending champion Scottie Scheffler battled through a neck injury to improve to eight under.
Rory McIlroy mixed five birdies with four bogeys and a double bogey as he slipped back to six under with a 73.
The world number two, who was joint overnight leader with Clark and Schauffele, is eight shots off the lead despite making 15 birdies in his opening 36 holes. Clark had 16 birdies in his opening two rounds.
McIlroy struggled to match the control he showed on Thursday as he scrambled his way around the iconic Sawgrass course.
He had three bogeys and three birdies in his opening six holes then another birdie on the ninth was cancelled by a bogey on the 12th.
Although the Northern Irishman knocked in a 16-foot birdie putt on the next, a wayward drive into sand led to two more shots going on the 14th.
While he toiled, Scheffler showed remarkable resilience to post five birdies in 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 on 12 and that’s when I could barely get the club back. So I got some treatment, maybe it loosened up a tiny bit, but most of the day I was pretty much labouring.
“I did what I could to stay in the tournament and hopefully it’ll loosen up and then I’ll be able to make somewhat normal swings.
“The way I was getting around the course, the way my neck was feeling, I didn’t know if I was going to be able to continue playing, so yeah, good fight out there.”
The 28-year-old, who won last week’s Arnold Palmer Invitational by five shots, is looking to become the first player to win successive Players titles in the 50th staging of the PGA Tour’s flagship tournament.
But he will go into Saturday’s third round six adrift of Clark, who won earlier this season at Pebble Beach.
Clark holed five birdies in six holes to edge clear of the field and knocked in two more in his final four holes to take control of the tournament.
“My iron play’s been very solid, I’ve rolled in a handful of putts and then I’ve really been mentally strong, so I’d say all of those things are why I’m sitting where I am right now,” said the American.
Fitzpatrick, the man Clark succeeded as US Open champion, built on his opening round of 66 by charging into the lead on 10 under with four birdies in six holes around the turn.
But he chunked his second from deep rough into water on his 13th hole as he dropped two shots. A birdie on the par-five ninth, his last hole, saw him sign for a 69.
“Anything can happen over the weekend, so it’s just about trying to stay patient, just 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 on 10 under late in the day by Canadian Taylor, who birdied the 15th and 16th holes as he carded a 68.
And Open champion Brian Harman catapulted himself into contention with a 65 to move to seven under.
The infamous 17th claimed yet more victims, with Beau Hossler hitting the 1,000th ball in the history of the tournament – since it moved to Sawgrass in 1982 – into the water that almost surrounds the green of the par-three hole.
England’s Justin Rose also fell foul of the hole. He was in contention to make the cut when he stood on the tee on one under but put two balls in the lake as he made a ruinous quadruple-bogey seven that sent him to three over par.
Two players will return on Saturday to complete their second rounds after darkness curtailed play once again but both have chances of making the cut, which is set to exclude all those at level par or worse.
That means Rose will join the likes of American duo Jordan Spieth and Justin Thomas in missing the final two rounds.
However, Japan’s Ryo Hisatsune will tee off on the par-five ninth, his final hole, on level par, knowing he must at least make birdie to make the cut.
Canada’s Ben Silverman has a more outside shot. He is at one over but has played two shots on the ninth and must hole from 109 yards for eagle to make the weekend.