A blistering round of 64 from Jim Furyk put the American in control at the halfway stage of the Tour Championship at East Lake - the final tournament of the FedEx Cup.
Furyk, one of Davis Love's wildcard picks for next week's Ryder Cup, fired six birdies in an outward 29 to storm to the top of the leaderboard in the 30-man field.
The American, who won the FedEx Cup two years ago, looked to have a chance of a 59 when he had seven birdies in the first 10 but he couldn't maintain that blistering pace.
More birdies came at the 15th and 17th, but there were also bogeys at the 13th, 16th and 18th as he finished on seven under par.
"For me the back nine plays quite a bit tougher," the 42-year-old said. "I stumbled a bit again, but I've got myself back in the hunt.
"When I'm playing well I can play on any course and here there's more of a premium on keeping the ball in play."
Level coming home, Furyk's effort was enough for a one-shot lead over England's Justin Rose, who rolled in a birdie putt at the last to earn a spot in Saturday's final pairing.
Americans Bubba Watson and Bo Van Pelt are a further shot back while world number one Rory McIlroy carded a 68 to be four shots off the pace.
He had a lucky break on the 10th, hooking his drive against a fence but being given a free drop because of ground under repair, with the highlight being an eagle three at the 15th.
But despite being in tied seventh, he's still projected to win the FedEx Cup and scoop that massive $10m bonus fund.
Joint first round leader Tiger Woods resumed with an untidy bogey after pushing his approach to the first into a bunker and his birdies at the third and seventh both came after he had driven into more sand.
He missed the green at the next, fluffed a chip and double-bogeyed, came back with a birdie, but then dropped more strokes at the 11th and 12th.
With further bogeys at the 16th and 17th only Nick Watney and Ernie Els were worse than Woods' 73 on the day. Tiger will go into the weekend six back.
Luke Donald shot 69 to stand level par at halfway, but with a 73 Lee Westwood was 28th in the 30-man field on five over - not exactly what he was looking for a week before the Ryder Cup in Chicago.