Australian Robert Allenby is not ready to concede defeat even though he is six strokes behind leader Sergio Garcia after the third round at the $US7 million ($8.4 million) Tour Championship.

"I still think I can win. I'm a fair way back but you never know," he said after compiling seven birdies in an impressive three-under-par 67 at demanding East Lake.

Allenby is equal fifth, while Spaniard Garcia (67) leads at eight-under 202, three strokes clear of Americans Phil Mickelson (69) and Anthony Kim (72).

Allenby was near last after an opening 75, but he has worked his way to the edge of contention with a fine display of shotmaking.

"I like the way I'm hitting it," he said after sinking a sharply breaking 2.5-metre putt to salvage par at the last.

"I played nicely, aggressively when I could, and just tried to make as many birdies as I could, knowing that you are going to make some bogeys out there."

Stuart Appleby, the only other Australian in the 30-man field, is out of contention, 11 strokes behind after a round of 70.

Garcia, meanwhile, started the day two strokes behind halfway leader Kim, but gained a measure of revenge for last week's Ryder Cup, where the American won their singles match on the final day.

"I hit a lot of good shots early on and the putts didn't want to drop. Fortunately, a couple dropped later in the round," Garcia said.

Kim had a horrible day with the driver, finding just four fairways.

One of his errant tee shots, at the par-five ninth, struck a male spectator on the forehead, leaving an enormous gash.

"I thought I killed him," Kim said. "It was awful to see a golf-ball sized impression in his forehead and it was cut open."

The man was treated by medics and appeared to be dazed but okay.

AAP