British Open champion Phil Mickelson flirted with a 59, but settled for an eight-under-par 63 and a share of the first-round lead on Friday alongside England's Brian Davis at the PGA Tour's Deutsche Bank Championship in Massachusetts.
Mickelson had eight birdies and an eagle along with two bogeys to set the early pace, and Davis joined him atop the leaderboard with a blemish-free round that featured eight birdies.
They were one stroke in front of American Kevin Stadler, with Spain's Sergio Garcia and Americans Hunter Mahan and Roberto Castro a further shot back on 65.
A group of 16 players on five-under 66 included England's Lee Westwood and Ian Poulter, South African Ernie Els, Sweden's Jonas Blixt and 2009 British Open champion Stewart Cink of the United States.
Mickelson was the class of the morning, teeing off on the 10th hole at TPC Boston alongside world No.1 Tiger Woods and Masters champion and No.2-ranked Adam Scott.
He birdied seven of his first nine holes. A bogey from a bunker at the first was followed by an eagle three at the par-5 second, where his second shot landed two feet from the pin. He nabbed another birdie at the par-3 eighth, but closed with a bogey when he hit his tee shot at the ninth into thick brush on the right.
Woods, who battled back pain in a runner-up finish to Scott at The Barclays last week, carded a three-under-par 68 that included four birdies and a bogey.
He said his back was "all good" especially after an extra day off because of the tournament's Friday start. The event, the second of four in the US PGA Tour's season-ending playoffs, will end on Monday - the US Labor Day holiday.
"It helped having that extra day off," Woods said. "It made a difference.
"I didn't hit the ball as well as I'd like to, but I scored all right," he added. "I didn't give myself a lot of looks."
Things were even more of a struggle for the third man in the group, as Scott battled to a two-over 73.
The Aussie went two-over with bogeys at the 10th and 14th, picked up his only birdie at the par-3 16th, then gave the shot back with a bogey at the par-4 sixth.
Jason Day was the best-placed Australian after shooting a four-under 67 to be tied with Brian Gay, Henrik Stenson, Graham DeLaet, Jordan Spieth, Boo Weekley, Robert Garrigus, KJ Choi, John Merrick, Charl Schwartzel and Brendan Steele.
Defending champion Rory McIlroy, trying to turn around a disappointing season carded a one-under 70 that he called "sloppy".
"I'm making a lot of birdies, but also making a lot of stupid little mistakes," said McIlroy, who is without a win in 2013. "If I can cut those out, it's a different story."
