Henrik Stenson fired four birdies and an eagle in a six-under par 65 on Sunday to seize the third-round lead in the Deutsche Bank Championship.
The Swede`s 13-under total of 200 was one stroke in front of American Rickie Fowler, with American Sean O`Hair and Aussie Matt Jones a further stroke back on 202 after a day when world number one Rory McIlroy and PGA Champion Jason Day were unable to make a move up the leaderboard.
"It was a good day out there," Stenson said. "I was striking it nicely today."
Day, the world number three who came into the tournament with a chance to supplant McIlroy atop the rankings, had a double-bogey, three bogeys and three birdies in a two-over 73 that left him tied for 25th on four-under 209.
"There`s no excuse for poor playing," said Day, who saw a run of 22 straight rounds of par or better end. "I just wish I had a little bit more energy."
McIlroy, playing his second tournament since he was sidelined by an ankle injury in July, remained at 2-over after an even-par 71 at TPC Boston that included three birdies and three-bogeys.
McIlroy, winner of the 2012 Deutsche Bank title, birdied the par-five 18th to avoid a second straight over-par round.
But his inability to mount a challenge means Masters and US Open champion Jordan Spieth could again grab the number-one world ranking, even though the 22-year-old American missed the cut on Saturday and won`t be around for the Labor Day holiday finish on Monday.
If Day doesn`t win, and McIlroy finishes outside the top 10, Spieth could still regain the summit he reached with a runner-up finish at the PGA Championship and held for two weeks.
"It`s a mathematical system with algorithms and all sorts of different things," McIlroy said of the two-year rolling points formula for determining number one. "It`s not something I really worry about."
Stenson, runner-up to Day last week at the Barclays, is gunning for a second Deutsche Bank title. He won the event in 2013 on the way to winning the US PGA Tour`s FedEx Cup playoff title and its $10 million bonus.
"It`s always good to be back at a course where you`ve performed well and played well," Stenson said. "I`ll just try to keep it going."
He had three birdies on the front nine plus an eagle at the par-four fourth hole.
"Set it off straight on line with the pin, which I was trying to do," Stenson said of his three-wood off the tee at the fourth, which left him a tough 20-foot putt. "It actually worked out perfectly."He parred the first eight holes of the back nine before rolling in a tough birdie putt at 18 that gave him the outright lead.
"I left myself a few good chances on the back nine, I just couldn`t convert," said Stenson, who was pleased to keep a bogey off his card with a two-putt par at the par-three 16th. "Then the nice birdie on the last."
Fowler carded a 67, saving birdie at the last to stay within one stroke of Stenson despite finding only four of 14 fairways.
O`Hair carded a 67 and Jones a 68 for 202. They were one stroke in front of Scotland`s Russell Knox, who posted a 68 for 203.
Charley Hoffman, who started the day with a three-shot lead after a second-round 63, fell six adrift after a five-over 76.