US Tour:Tiger Woods produced a stunning front nine to build a three-shot lead after the second round at the $7 million Tour Championship in Georgia.

Woods picked up seven shots in a six-hole purple patch on the outward half at East Lake, making the turn in just 28 in perfect scoring conditions.

He needed to come home in only 31 to shoot the magical 59 and, the way he was playing, seemed likely at the very least to challenge his career best score of 61.

However, he was not the same after the turn, and a bogey at the par four 12th, where he plugged his approach shot in a greenside bunker, put paid to any thoughts of a 59.

Woods subsequently birdied the par five 15th, bogeyed the 16th and birdied the last for what surely must rank as the most disappointing 63 of his life.

"I didn't know I shot 28 on the front nine until we got in the scoring tent," Woods said.

"I don't know if I was in a zone or not. I just felt that the rhythm was good."

He posted a 13-under 127 halfway total, with Woody Austin (65) alone on 10 under, and defending champion Adam Scott (66), first round leader Tim Clark (69) and veteran Mark Calcavecchia (66) another shot back.

Sergio Garcia (64) heads the small European contingent, five shots off the pace, with Padraig Harrington (70) another stroke behind.

Harrington, who shot a seven-under-par 63 in the first round, failed to keep up the momentum and is tied for eighth place on 133.

With the greens abnormally soft after yesterday's heavy rain, the course was there for the taking, and no one took advantage of conditions better than Woods.

He started slowly, only parring the first three holes, before making five successive birdies, followed by the eagle at the ninth.

He holed a 10-footer at the par four fourth, before holing a 60-foot bunker shot at the fifth.

His next three birdies came from 13 feet, 11 feet and seven feet respectively, before he got home in two from the fairway of the par-five ninth and drained a monster, 70-foot putt.

"Pure luck," he said of his unlikely eagle. "If you could have been right behind the ball and seen how that thing was bouncing all over the place, it was actually quite funny.

"It was left of the hole, right of the hole, left of the hole, right of the hole, and then it went in.

"I knew at that time I had a three-shot lead over Woody, and I just wanted to make sure I could increase that on the back nine.

"If felt if I shot under par I would, but two bogeys kind of derailed that."