Spieth did his best Jekyll and Hyde impersonation en route to a 4-over-par 74 in the first round of the Barclays on Thursday. If he finishes outside the top 60 this week, he could lose his No. 1 ranking to McIlroy, who decided not to play this week to rest up for the Deutsche Bank Championship in Boston over Labor Day weekend.
In a schizophrenic round that saw the two-time major champion shoot 2 under on his first nine holes, but 6 over on the second nine, Spieth felt he could turn it around as quickly as Friday's second round.
"I would argue that this was ... After the tee shots, this is the worst round I've played in years, for hitting that many fairways," said Spieth, who found the short grass off the tee on his first 11 driving holes but none of the last three. "I'll just take it at that, that it's just a fluke."
The 22-year-old Spieth hasn't missed a cut in more than three months and he has missed playing the weekend just twice in 21 starts so far this season.
Starting on the 10th hole, Spieth couldn't have played a more concise, scripted opening nine. After a birdie on No. 10, Spieth had several good looks to get deeper into red numbers, but he failed to do so until he drained a 16-foot putt on the par-5 16th to get to 2 under.
After birdie putts on Nos. 17 and 18 burned the edges of the cup, shortly thereafter, everything came undone. He started the front nine -- his back nine -- bogey-bogey-double before righting the ship with a birdie on the par-4 fourth hole. But three bogeys in his last five holes -- including a 3-putt on No. 9 to a hole location that looked like it was on the side of the hill -- ended his day north of 100th in the field of 120.
"Just lost a little bit of focus, and again, I'm just going to take it as -- all in all, I'm just going to take today as a fluke round," said Spieth, who tees off for the second round at 1:06 p.m. ET on Friday. "I still believe I'm playing well. It just happened to be an off-day on a day where it counted."
Spieth's group Thursday included Watson and Jason Day (68). For Spieth and Day, it was the first time teeing it up alongside each other since the final pairing at Whistling Straits in the PGA Championship 11 days ago, where Day won his first major championship.
Watson wasn't hitting all the fairways, but at times that was to his advantage. The greens are pitched in such a way that some shots have to carry to the hole, allowing for spin to make sure it stays below the hole. That's what caused Spieth problems.
From the rough, Watson was able to land short of the flag and have it roll up toward the hole. That set up ample birdies.
Ditto for Finau, the power Utah rookie.
"So No. 9 today with that pin just on top of the ridge, if you draw a decent lie in the rough, it's almost easier to just run something up instead of worrying about the spin if you're hitting from the fairway," Finau said.
He had the wildest round. Finau opened with three straight birdies, followed with three straight bogeys, made one par and then ran off three more birdies.
Villegas only got into the top 125 to qualify for the playoffs last week at the Wyndham Championship, with two shots to spare. That was pressure. Now he feels as though he has nothing to lose as he tries to get into the top 100 who advance to the second event next week at the TPC Boston.
"Last week was an important week," said Villegas, who is No. 123. "It hasn't been the best of years, and just to be able to sneak in here and give myself a chance ... I get off to a good start, and three more rounds to go and keep it going."
Levin secured his spot in the playoffs with a 63 in the final round at the Wyndham, moving up seven spots to No. 115. Much like Villegas, he felt relieved to have made it to The Barclays, and everything else is gravy. He rolled in three early birdies and dropped only one shot on a mild, blustery day.
"This is a nice stress to have," he said. "I'm happy with where I am right now and who knows? Maybe I can keep it going."
Day pulled out of the pro-am Wednesday after tweaking his back. Oddly enough, he had wanted an MRI on his back before the playoffs to make sure everything was in order. He felt the twinge removing a light box from under his motor home, and decided to have the MRI on Wednesday. It showed everything in good order, and while the PGA champion rubbed his back after a few hooked tee shots, he felt good enough.
The last time the Barclays was played at Plainfield Country Club, Hurricane Irene paid a visit to the area, shortening the event to 54 holes. That came after an earthquake earlier in the week. Dustin Johnson eventually won the title at 19 under par.
Information from The Associated Press was used in this report.