Jordan Spieth has missed the cut at The Barclays and is set to lose his status as world number one to Rory McIlroy.
Spieth, who shot his worst score (74) for three months at Plainfield Country Club on Thursday, could only do marginally better with a second round 73 after hitting five bogies, a double bogey and four birdies.
His surprise struggles mean that McIlroy, currently recovering from an ankle injury, will return to the top of the tree despite not lifting a club this weekend as a precaution.
There were no such problems for Bubba Watson, who now has a one-shot lead over the rest of the field after sharing a four-way tie at the top of the leaderboard following day one.
The American hit a sublime five-under 65 in the first round and backed it up with a solid 68 on Friday to nudge in front on seven under overall.
Colombia's Camilo Villegas and Americans Spencer Levin and Tony Finau had a share of the lead going into day two, but they all struggled to maintain that pace.
Finau is the highest-placed out of that trio, but a bogey on the 16th scuppered his hopes of staying toe-to-toe with Watson and he sits one shot back in a four-strong cluster on six under.
There he is joined by Sweden's Henrik Stenson, who shot five birdies on the first 12 holes to push up the leaderboard, Zach Johnson and Jason Dufner.
Villegas is just behind on five under - where he is joined by Jason Bohn after the American hit six birdies in a blemish-free round to card the lowest score of the day (64).
Levin, meanwhile, is one of seven men on four under after hitting one-over par on Friday.
Spieth admitted he would need some time to work out where his week had gone wrong.
"Yeah, tough week," he said on the PGA Tour website. "I'm definitely searching for answers. I don't know exactly what I'm going to do from here as far as how I get prepared for next week but I have some time to figure it out. We don't start till Friday."
Despite the disappointment, Spieth, who remains top of the FedExCup rankings, swiftly turned his attention to the Deutsche Bank Championship as he downplayed the importance of the ranking.
"I've reached that peak already and I know it's going to be close enough to where if I just get the job done next week, I'll be back in that ranking," he said. "But again, that ranking, it's great once you reach it but it's not something that I'm going to live or die on each week. It doesn't really make much of a difference. If you go on a three- or four-year cycle, Rory is No. 1 in the world. If you go just base off of this year, I am. They just use two years.
"In my mind, it's just about trying to win the FedExCup at this point."