Henrik Stenson made another fast start then struggled in torrential rain over the closing holes to remain four strokes in front after Saturday's third round of the season-ending Tour Championship.
With the FedExCup playoff title and its bonus jackpot of $10 million also on the line at East Lake Golf Club, Stenson carded a one-under-par 69 in difficult scoring conditions to stay on track for all those honours.
The Swede, ranked second in the FedExCup points standings, raced to the turn in four-under 31 to briefly lead by nine strokes but dropped four shots on the back nine to post an 11-under total of 199.
Long-hitting Dustin Johnson, who narrowly squeezed into the elite field of 30 players, fired a 67 to sit alone in second place at seven under, two ahead of fellow American Steve Stricker (68).
FedExCup points leader Tiger Woods, seeking a sixth PGA Tour victory this season, was a distant 14 strokes off the pace after returning his first sub-par score this week, a 69.
"I didn't hit it very good today," Woods said after missing nine of 14 fairways and reaching only 11 of 18 greens in regulation. "I hit everything to the right or flipped it left, but I putted better."
The players teed off extra early on Saturday with tournament organisers concerned about heavy thunderstorms expected later in the day and Stenson made a sizzling start for the third consecutive round.
The in-form Swede, who won the Deutsche Bank Championship earlier this month, knocked in a three-footer to birdie the second and a 20-footer at the third to move seven strokes ahead.
Stenson's playing partner, Masters champion Adam Scott, tumbled out of contention with a 74 after falling ill. The Australian was suffering from flu and a high fever and was put on an intravenous drip before he teed off.
Stenson rolled in a seven-foot birdie putt at the seventh, then picked up another shot at the par-five ninth, where he chipped up to two feet, to reach the turn with a commanding nine-stroke lead.
As the rain intensified amid strengthening winds, the Swede dropped his first shot of the day at the 10th after missing the fairway off the teen and hitting his second back left of the green.
He also faltered at the 14th, his tee shot sailing way left for his ball to settle under a bush from where he had to take an unplayable lie, but limited the damage by sinking an 11-footer for bogey.
Stenson recovered with a birdie at the par-five 15th, getting up and down from a greenside bunker, and did well to salvage par at the tricky 17th where he rolled in a 15-footer.
However, he signed off with a three-putt bogey at the par-three last for his lead to be trimmed to four.
U.S. Open champion Justin Rose of England (70) and Americans Zach Johnson (69), Jordan Spieth (71) and Billy Horschel (70) were tied for fourth at four under.