Jordan Spieth fired a two-under-par 68 to earn a one-stroke lead over Henrik Stenson heading into the final day of the Tour Championship in Atlanta.
The American, 22, grabbed three birdies and a bogey to finish his third round on eight-under, one clear of the Swede, who led the way at East Lake for the first two days.
Stenson, without a PGA title this year, boasted a three-shot lead coming into Saturday, but a two-over-par 72 dented his chances somewhat.
England's Paul Casey and American Rickie Fowler sit four shots off the pace, with world number two Rory McIlroy one behind the duo, along with Zach Johnson.
World number one Jason Day, who has picked up two wins since ending his Major hoodoo at the PGA Championship in August, is eight shots back on level par.
Shane Callaghan
