Rose made birdie on half of his holes at Cog Hill, a tough course that played even longer in chilly conditions, giving him an 8-under 63 and a two-shot lead over Webb Simpson and Mark Wilson.
"Didn't expect that going out there today," Rose said. "I looked to the weather, looked at the temperature, and I thought today was going to be a day to hang in there. Little did I know I was about to play so well -- certainly my best round of the year by a long, long way. And could have been top five, top 10 rounds I've ever played for sure."
There were other reasons he didn't see it coming.
Since a solid spring through the Masters, the 31-year-old player from England lost his way and went 10 straight tournaments without a top-10 finish. He is No. 34 in the FedEx Cup, and because only the top 30 advance to the Tour Championship and a shot at the $10 million bonus, Rose figured he might as well give it his best shot.
It was better than he imagined.
He didn't miss a single fairway and only twice had to scramble for par.
One round made his prospects for the FedEx Cup brighten considerably, although plenty of other players took advantage of relatively soft greens that made up for the swirling breeze and temperatures that eventually climbed into the 60s.
Simpson remained hot despite the weather.
He won for the first time on the PGA Tour a month ago at Greensboro, then won again two weeks later in the Deutsche Bank Championship to move to the top of the FedEx Cup and assure himself one of the coveted top five positions at East Lake. Another week, another course, and there he is again.
"Luckily, I was able to keep the momentum in the good stretch I had in Boston going into today," Simpson said. "We got off to a really good start and made a few really good saves there in the middle of the round and finished with a couple birdies coming in. It was a good day for the tough course and tough conditions we were facing."
Simpson made it sound simple, which is how golf can feel when a player is winning.
It wasn't that way for everyone.
Dustin Johnson, the defending champion at Cog Hill, sputtered at the start and then stumbled at the turn, making five bogeys for a 40 on his back nine for a 76. Jason Day had a 77, while Bubba Watson was wild off the tee and didn't make a single birdie in his round of 78.
Phil Mickelson nearly joined them. He took double bogey on the par-3 second hole when his flop shot from the other side of the green only went one-third of the way toward the hole and stayed in the collar of the rough. Another towering flop shot wound up 12 feet by the hole. Lefty was 4 over through five holes, but ran off four birdies and salvaged a 72.
The measure of Rose's good round was that his 63 was nearly nine shots better than the average score in the opening round, and only 16 other players managed to break 70.
K.J. Choi opened with a 67, while the group at 68 featured Jim Furyk and Camilo Villegas, both of whom need a big week to advance to the Tour Championship. Villegas narrowly got into the FedEx Cup playoffs, starting at No. 109, and now has the Tour Championship in his sights.
"Who cares where you are right now," Villegas said. "It's all about just playing good golf from here the next three days and hopefully advancing."
Rose said he cleaned up his swing with coach Sean Foley during a practice session Tuesday, making sure the club was not laid off at the top of his swing. He found a simple swing though, stuck with it, and watched it pay off in a big way.
As for his position in the FedEx Cup? Rose didn't even bother to do the math.
"I've got nothing to lose this week," he said. "That's my strategy. That's my attitude. Right now, I'm not going to Atlanta. I've got everything to gain this week. That's really the way I'm seeing it. Guys who are 26, 27, 28, 29, who have played well all year, they might be pretty tense this week because they feel they deserve to be in Atlanta."