Bubba Watson coughed up a two-shot lead on the stroke advantage after three rounds of the Deutsche Bank Championship.
Watson, who won twice earlier this year, managed a one-under 70 to complete 54 holes at the TPC Boston at 11-under-par 202.
The big-hitting left-hander will go for his fourth PGA Tour win on Monday. Earlier in the year, he captured the Farmers Insurance Open and the Zurich Classic of New Orleans.
"I need to tie them tomorrow so that I win by one," Watson joked in a television interview. "I'm just going to come out here and keep doing what I'm doing, I'm just trying to play golf and not worry about what the lead is. Today, I had some bogeys and gave away some shots, but at the same time I made some putts to make some birdies."
Jason Day, who tied for second place last year, and Brendan Steele both carded four-under 67s to move into a share of second place at minus-10. They were joined there by Scott (71), Jerry Kelly (68) and Chez Reavie (68).
Last year's FedEx Cup champ Jim Furyk carded a five-under 66 to move into a tie for seventh at nine-under-par 204. He stands alongside Schwartzel (72), world No. 1 Luke Donald, Webb Simpson (67) and Gary Woodland (66).
The tour, as usual, is taking advantage of the Labor Day holiday by playing Friday-to-Monday. After an off-week, the top 70 on the FedEx Cup points list will continue the playoffs at the BMW Championship.
Among those needing big final rounds to get inside the top 70 are 2010 U.S. Open champion Graeme McDowell, John Rollins, J.J. Henry, 2012 U.S. Ryder Cup captain Davis Love III, Padraig Harrington, Ricky Barnes and Ben Crane.
Watson stumbled to a bogey on the first hole to fall two strokes behind Nick Watney, who birdied the first and eagled the second to jump to 11-under. Watson got a shot back with a birdie on the par-five second.
After Watney fell back to 10-under with a bogey on the fifth, Watson claimed a one-stroke cushion with a birdie on No. 4. Watney birdied the seventh to join Watson at minus-11, but Watson birdied the same hole to go one up again.
Watson birdied No. 10 to push his advantage to two strokes over Rickie Fowler, who had five birdies and a bogey in the first 11 holes.
After Fowler dropped a stroke on the 12th, trouble loomed for Watson as well.
He missed the green at the par-three 11th, leading to a bogey, and his drive on No. 12 found thick rough, which forced Watson to lay up. He played his third to 17 feet and he two-putted for a bogey, but was still alone in the lead as the others near him were also faltering.
After a pair of pars, Watson found a brutal lie in the rough on No. 15 and had to lay up again. He pitched his third to nine feet, but missed the putt to the left. His bogey led to a six-way tie for the lead at minus-10.
Watson answered with a nine-foot birdie putt on the par-four 17th to regain the lead. He had just over eight feet for birdie at the last, but was unable to convert that effort.
"When I made the turn, I made a good par on nine, birdied 10 and had a three- shot lead, or somewhere in that area," said Watson in an interview with the Golf Channel of his two-stroke lead on No. 10.
"I knew if I could put the gas peddle down, I could get a big lead. But I made back-to-back bogeys there. Coming down the stretch, I birdied 17, so I'm in good position overall."
Day had an eagle, a bogey and three birdies in his round, while Steele carded two eagles, two bogeys and two birdies for his second straight 67.
Scott traded a birdie for a bogey on holes two and three, then a bogey for a birdie at 17 and 18. Kelly and Reavie both had four birdies and a lone bogey in their rounds of 68.
Phil Mickelson, the 2007 champion, got his belly-putter going on Sunday. He collected six birdies to go with a hole-out eagle on the par-four 11th for a round of eight-under 63. The low round of the day helped Mickelson jump into a share of 19th at minus-seven.
NOTES: Watson owned the 54-hole lead for the fourth time on the PGA Tour. He lost the first two, but claimed a playoff victory over Simpson earlier this year at the Zurich Classic...If Watson can pick up the win, he would likely take over the top spot in the race for the FedEx Cup...There are 23 players within four shots of Watson's lead heading into Monday's final round.