Norton - South Africa's Louis Oosthuizen fired an eight-under par 63 on Sunday to seize a three-shot lead after three rounds of the PGA Tour's Deutsche Bank Championship.
Oosthuizen, the 2010 British Open champion, birdied seven holes in a row starting at the par-four fourth, and followed up his lone bogey of the day at 17 with a birdie at the par-five 18th at the par-71 TPC Boston.
He had a 54-hole total of 19-under par 194.
Oosthuizen surged past overnight leader Rory McIlroy, the world number one from Northern Ireland who carded a 67 for 197.
Tiger Woods carded a 68 for a share of third place on 13-under 200 alongside fellow American Dustin Johnson, who posted a 65.
Oosthuizen, who trailed McIlroy by one coming into the round, made it look easy. His string of seven birdies included four putts of 20 feet (six meters) or more, the seventh coming with a tap-in at the par-four 10th.
His seven-under 29 on the front nine was a tournament record, as was his 54-hole total.
"Louis put on a display right there," said McIlroy, who nevertheless wasn't conceding defeat.
"I've come from farther behind before... It's going to be an interesting day tomorrow(Monday)."
The $8 million tournament, which is the second stop on the US tour's four-event playoff series, concludes on Monday, the US Labor Day holiday.
McIlroy, who claimed his second career major title at the PGA Championship in August, opened with back-to-back birdies.
Playing alongside him, Oosthuizen also birdied the second but didn't begin to pull away until the fourth.
He drained a seven-footer to launch his run and after 20-footers at five and six made a short birdie putt at seven after a good shot out of the rough right of the green.
He drained a 40-foot bomb at the eighth and a 23-footer at the ninth.
"Every putt had perfect speed," he said. "I told Rory, 'Sorry, but you've got to take it when you can.'"
With the putts dropping, Oosthuizen could afford to be aggressive.
"I went at most of the pins," Oosthuizen said. "Once I started getting birdies, making putts, I started going at the pins because my swing felt great, and after 10 holes being 8-under, you always think about getting it to 59. I didn't do anything different from there on in."
McIlroy finished with six birdies and two bogeys, two of his birdies coming in the last three holes to keep Oosthuizen from getting even further away.
Woods had a relatively quiet day, but did enough to keep himself in the hunt.
He said that Oosthuizen's round, and the 63 of Keegan Bradley, showed what would be needed.
"I'm going to have to put together one of those rounds," Woods said.
"It won't surprise me if somebody shoots 8- or 9-under par tomorrow because of where the pin locations are. Somebody is going to go out there and do it. It may be early, it may be late, who knows? But hopefully, I'm one of those guys."
Leading third-round scores on Sunday from the $8 million Deutsche Bank Championship (USA unless noted, par-71):
194 - Louis Oosthuizen (RSA) 66-65-63
197 - Rory McIlroy (NIR) 65-65-67
200 - Dustin Johnson 67-68-65, Tiger Woods 64-68-68
202 - Bryce Molder 65-69-68, Ryan Moore 64-68-70
203 - Jason Dufner 67-66-70, Charley Hoffman 67-67-69
204 - David Hearn (CAN) 67-69-68, Phil Mickelson 68-68-68, Jeff Overton 64-71-69, D.A. Points 68-65-71, Brandt Snedeker 69-70-65
205 - John Senden (AUS) 66-69-70, Webb Simpson 69-70-66
206 - Jim Furyk 69-72-65, Adam Scott (AUS) 69-69-68, Steve Stricker 69-69-68
207 - Keegan Bradley 71-73-63, Matt Every 71-68-68, Nick Watney 72-69-66
208 - Chris Kirk 63-70-75, John Merrick 68-72-68, Seung-Yul Noh (KOR) 62-71-75, Kevin Stadler 68-71-69, Lee Westwood (ENG) 68-71-69
209 - Luke Donald (ENG) 67-72-70, Ernie Els (RSA) 69-69-71, Tom Gillis 69-69-71, Troy Matteson 72-67-70, Ted Potter 69-68-72