Brett Wetterich fired a five-under 66 on Sunday to claim a one-stroke lead after the third round of the US$7 million Deutsche Bank Championship.
Wetterich posted his best round since June as he moved to a 13-under 200.
He was one shot in front of fellow American Arron Oberholser, who also carded a 66 for 201.
Wetterich, whose only PGA Tour victory came at the Byron Nelson Classic last year, eagled the par-five seventh to take the lead and maintained it despite missing a pair of short putts at 16 and 18.
After seizing a share of the lead halfway through the round, Tiger Woods had an uncharacteristic late stumble, three-putting the final two holes, to finish with a 67 in the second tournament of the inaugural FedEx Cup playoff series.
Woods was three shots off the lead at 203.
Phil Mickelson failed to capitalize on a couple of spectacular shots but he regrouped to birdie 18 to finish with a 68 and move into sole possession of third place on 202.
Woods appeared ready to assume control of the tournament midway through the round.
After an opening-round 72 left him nine shots off the lead, the world's No. 1 player rebounded with a 64 on Saturday to get in contention and continued his move up the leaderboard early in the third round.
Woods birdied the second, then birdied three in a row from the eighth to move into a tie with overnight co-leader Aaron Baddeley and Wetterich.
Another birdie at No. 12 got Woods within a shot of Wetterich, but he suffered a three-putt bogey on the 17th and had to settle for a par on the par-five 18th after another three-putt.
Mickelson almost holed out from the fairway at 14, but missed a short birdie putt, then hit the flagstick from the fairway on 15, only to watch the ball bounce off the green.
After carding 10 straight pars, Mickelson hit a beautiful approach shot on 18 and converted the short putt for a birdie.
RSS