Kenny Perry upstaged overnight leader Tiger Woods in Georgia to lead the Tour Championship by two strokes going into the last round of the PGA Tour's FedEx Cup finale. Ireland's Pádraig Harrington, Woods' playing partner in the final group, began the day a shot behind the world number one but three-birdies and four bogeys led to a 71 and left him five shots off the pace at three under.

Veteran American Perry began the day at two under par, three shots off the pace set over 36 holes by Woods, who leads the season-long FedEx Cup standings and will be guaranteed a €6.8million bonus if he picks up the €920,000 winner's cheque.

Harrington can still secure the big prize but needs to win and hope Woods finishes third or worse. But he now has Perry to worry about too.

Instead of the expected march towards that goal by Woods, Perry outscored the world number one by five shots, his six-under-par 64 at East Lake Golf Club in Atlanta taking him to eight under par for the tournament.

Perry, 49, will now go head to head with Woods, who shot a 69 in the final pairing, needing a victory and his playing partner to finish fourth or worse if he is to swipe the mega-money prize from the grasp of the best player in the world.

World number three Phil Mickelson may also have a say in the matter, his five-birdie, one-bogey 66 continuing his upward mobility following an opening 73 by taking him to four under par after 54 holes.

That puts the left-hander in a tie for third place with fellow American Sean O'Hair, the first-round leader whose double bogey at the par-four 17th left him with a third-round 70.

World number two Steve Stricker, who started the tournament second in the FedEx Cup standings, is at two under following a 66 that returned him to the mix after a second-round 72. Stricker is tied for seventh with South Africa's Ernie Els, who followed a Friday 66 with a one-over 71.

With play brought forward by more than three hours in a bid to beat heavy rain forecast later in the day for the Atlanta area, Perry opened his third round in a hurry himself.

A year on from his Ryder Cup heroics in his home state of Kentucky, Perry sank birdies at his first four holes on the par-70, 7,154-yard course in a bid for some personal glory.

A bogey at the par-three sixth checked his progress but he rebounded with another birdie at the par-four seventh to make the turn in 31, in a share of the lead with Woods and Harrington, who were experiencing rollercoaster rounds.

Paired once more with the Irish three-time major winner, Woods saw his lead disappear at the first hole as Harrington birdied but then edged back in front with a birdie of his own at the par-three second.

The nip and tuck continued as Harrington birdied the third, only to post back-to-back bogey fives at the fourth and fifth holes.

Then Woods wobbled, bogeying the seventh and 10th holes as Harrington birdied the eighth, but the world number one got back to level par for the day, five under for the tournament, with a birdie at the 11th.

Their private duel was eclipsed, however, as Perry took birdies at the par-three 12th and par-five 15th to move into a three-shot lead over Woods and O'Hair at eight under par, with Harrington falling back into a tie for third at four under following a bogey at the par-four 12th.

Woods clawed a shot back with a birdie of his own at the 15th but there was more trouble for Harrington, who bogeyed the 17th on his way to a 71

England's Luke Donald had a bad day at East Lake, an eight-over-par 78 sending him tumbling down the leaderboard to 29th place at nine over while Australia's Geoff Ogilvy moved in the other direction, climbing from last place in the 30-man field to a tie for 17th with a third-round, six-under-par 64.

Perry said: "When you open up with four birdies in a row, that don't happen a lot, especially on this golf course. I knew it was going to be a special day.

"I had such a good feeling, a good vibe, after those first four holes. I was relaxed and I knew it was going to be a good day.

"I was in that zone and it was just a very comfortable round of golf.

"I need to recreate that tomorrow, there's a lot on the line."

Woods said: "I hit the ball well today but it was very confusing on the greens. But I feel good (for the final round), I just need to hit a few putts."