Jim Furyk, hunting his first PGA Tour victory in two years, took advantage of a sizzling start to set the early clubhouse lead in the second round of the Tour Championship, while Rory McIlroy is still in the hunt.
Tournament favourite McIlroy carded a two-under-par 68 to stay on track for FedExCup play-off honours and the mind-boggling bonus of $10 million.
Furyk birdied seven of the first 10 holes on the way to a best-of-the week 64.
On a steamy day at East Lake Golf Club, American Furyk scorched the front nine in six-under 29 with a stunning display of pinpoint approach shots before finding the going much tougher after the turn.
He offset birdies at the 10th, 15th and 17th with bogeys at the 13th, 16th and par-three last to post a seven-under total of 133 in the PGA Tour's fourth and final playoff event.
Masters champion Bubba Watson birdied two of the last three holes for a 66 to finish at five under, one ahead of fellow long-hitting American Dustin Johnson (67).
Northern Irishman McIlroy, who is bidding for a fifth PGA Tour victory this year, and his fourth in just five starts, was a further stroke back at three under.
Twice winner Tiger Woods, co-leader overnight with Britain's Justin Rose in the elite 30-man field after opening with a 66, was four strokes off the pace with five holes to play.
Furyk has not triumphed on the PGA Tour since he clinched the Tour Championship and FedExCup honours in 2010 and to complete the 'double' this week he needs a lot to go his way.
Among several requirements, FedExCup points leader McIlroy would have to finish 12th or worse and second-ranked Woods fifth or worse.
Any of the top five players in the standings would secure the playoff title by winning the Tour Championship on Sunday - and that quintet comprises McIlroy and Americans Woods, Nick Watney, Phil Mickelson and Brandt Snedeker.
However, McIlroy remained in overall control of FedExCup honours after eagling the par-five 15th on the way to a 68 that also included a birdie and a bogey.
"I'm only four shots back, so I've still got a good chance going into the weekend," the 23-year-old said.
"First and foremost, I just have to try to think of my standing in this golf tournament, not really think about anything else.
"If it comes down to it on Sunday where I need to really know what I have to do for the last few holes, then if I have a decision to make between protecting my lead in the FedExCup or trying to win the golf tournament, I think I know what I'm going to choose.
"But we just have to play until we reach that point. At the minute, I'm just concentrating on trying to play as well as I can."