Patrick Cantlay's three-under-par 67 kept him two strokes clear of hard-charging world number one Jon Rahm on Thursday in the first round of the PGA Tour Championship.
Cantlay was staked to a two-stroke lead at 10-under par under the staggered-start system for the season finale after topping the tour's playoff standings thanks to his playoff win over Bryson DeChambeau in the BMW Championship on Sunday.
His four birdies on the day included a chip-in at the third and a two-putt birdie from 54 feet on the fringe at the par-five 18th at East Lake in Atlanta, Georgia.
At 13-under, he was two clear of Spain's Rahm, who holed out from the fairway for birdie at the first on the way to a five-under-par 65 that put him at 11-under.
Rahm rolled in a 22-footer at the fourth and a two-footer at the sixth.
He bounced back nicely from bogeys at the seventh and eighth with birdies at 12 and 13 before capping his round with birdies at 17 and 18.
"Played really good 14 holes, and then I think there was a bit of a slump on seven through 10, but I was able to manage really well those.
"The up-and-down for bogey on eight, the up-and-down for par on nine, and the up-and-down for par on 10 were key three in a row to limit the mistakes or the damage and from then I played amazing golf."
Rahm said the chip-in at the first got him going, but the tough long putt at the second was an even bigger confidence-builder.
"It was a great round except a couple of errors, but that's why we practice short game."
Rahm, who started the round four shots back based on his spot in the playoff standings, said he didn't think too much about the format.
"It's very easy to get caught up on how far back you start," he said. "I don't think I really once thought about it out there. I was just trying to post a score.
"My job is to hit the best shot I can each time and that's all can I control - 72 holes, it's a lot of holes and four shots is not that much (to make up)."
Cantlay also said he tried not to focus on the fact that he was handed a lead before hitting a shot, putting him in pole position to claim the win and the $15 million playoff champion's bonus.
"What goal I really have for this week is being process-oriented and being very present," he said. "I think being in the spot that I'm in, it would be easy to get ahead of yourself and easy to maybe stray from your game plan because you feel like you're ahead, and that's just not helpful.
"So I'm not going to do that."
Americans Harris English and DeChambeau were tied for third on eight-under, DeChambeau carding a one-under 69 and English a four-under 66 that included a hole in one at the par-three 15th that he followed with birdies at 16 and 17.
Until the 15th, English said, he'd been largely spinning his wheels. But after he watched playing partner Abraham Ancer come up a bit short with a four-iron off the tee he told himself: "Man, I can smoke this five-iron because I'm about a club longer than him and it came off good and rolled nicely.
"I don't know how loud I got," he said of his celebration. "I kind of blacked out there for 15 seconds. I know my caddie was pumped."
Another three players, Viktor Hovland, Cameron Smith and Justin Thomas were tied at seven-under heading into Friday's second round.
Patrick Cantlay 67
Jon Rahm (ESP) 65
Harris English 66, Bryson DeChambeau 69
Viktor Hovland (NOR) 66, Cameron Smith (AUS) 68, Justin Thomas 67
Kevin Na 66, Tony Finau 72
Billy Horschel 65, Brooks Koepka 67, Jason Kokrak 67, Dustin Johnson 68, Louis Oosthuizen 68, Jordan Spieth 69, Abraham Ancer (MEX) 69
Scottie Scheffler 67, Corey Conners (CAN) 67, Xander Schauffele 68, Rory McIlroy (NIR) 68