Masters and US Open champion Jordan Spieth's initial reign as world number one ended after two weeks when the 22-year-old American missed the cut at The Barclays.
Spieth added a three-over 73 that included a one-stroke penalty for stepping on his ball in a hazard to his opening 74 to finish five shots from the cut, which was set at two over par at Plainfield Country Club.
"Yeah, tough week. I'm definitely searching for answers," said Spieth.
"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 until Friday."
As for losing his number one ranking, a career goal of his, in such a short time, Spieth said: "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.
"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."
McIlroy was not competing in The Barclays, deciding instead to rest and strengthen the injured ankle that kept him from trying to defend his British Open title last month.
Two-times Masters champion Bubba Watson rolled in a 12-foot birdie putt at the last to claim a one-stroke lead.
Watson snapped a five-way tie for the lead with the birdie that gave him a two-under-par 68 at Plainfield Country Club for a seven-under 133 total.
Tied for second at The Barclays were British Open champion Zach Johnson (65), Sweden's Henrik Stenson (66) and Americans Jason Dufner (68) and rookie Tony Finau (69) on a warm, sunny day on the Donald Ross designed layout.