Padraig Harrington produced a barnstorming finish to card a brilliant seven-under-par 63 in the rain-delayed opening round of the Tour Championship in wet, wet Atlanta on Thursday.

The Open champion took advantage of ideal conditions after a three-hour rain delay, picking up birdies at the final four holes to come within one shot of the East Lake Golf Club course record - and the lead.

He was one stroke behind South African clubhouse leader Tim Clark who tied the East Lake course record with an 8-under 62 that left nobody especially surprised on a day when only 10 players in the 30-man field finished.

The greens, already soft as officials tried to nurture them back to life from a heat wave, turned into sponges after the three-hour storm delay and enabled the elite 30-strong field to take aim at every flag.

Clark's round was highlighted by an unlikely eagle at the par-five 15th, where he pitched in from 60 feet out of a horrible lie in the gnarly rough.

Harrington, who completed 12 holes before the delay, came out firing on all cylinders. He had a tap-in birdie at the par-five 15th before sinking a 15-footer at the par-four 16th.

He then jammed home 10-footers at the final two holes to negotiate the back nine in 29 strokes.

"I don't think I would have been capable of doing this if I played last week," said Harrington, who skipped a play-off event, citing tiredness.

"I wouldn't say I was in 100% top form out there but I was mentally sharp to make the most of a lot of things.

"I did a lot of good things, and that's the sign of a player who's fresh."

Meanwhile, Tiger Woods made a good start, four under after 11 holes, while England's Justin Rose was two under after 15 holes, with Spaniard Sergio Garcia two under through 13 holes.

Woods, who hit his approach shot to the first green shortly before bad weather halted play for three hours, could do nothing wrong for a while when play finally resumed.

His putter running hot on the soft, slow greens, he birdied the first three holes, just about the perfect start in his quest to win the 10 million US dollar bonus awarded at the end of the week to the FedEx Cup play-off winner.

Woods leads the points list, with fellow Americans Steve Stricker and Phil Mickelson his only realistic challengers.

Harrington was out in the first group of the day and, not for the first time, he was not introduced as the Open champion.

"From Dublin, Ireland, Padraig Harrington," said the starter, economical in his words.

But Harrington did not let that bother him, hitting a fine approach shot at the par-four first, only to miss his five-foot birdie putt on the high side, apparently reading too much break.

He then hit a shocking tee shot at the par-three second, 20 yards right of the hole, but a deft pitch led to a tap-in par.

He followed with a birdie at the par-four third, sinking a nine-footer after a nice approach shot from the left rough, but gave back the shot with a bogey at the par-four fourth, where he three putted.

Harrington's next birdie came at the par-three sixth, where he judged his tee shot beautifully to within six feet, and he parred to the turn.

He birdied the next two holes as his putter caught fire, running in an 18-footer at number 10 followed by a 12-footer at number 11.

It only got better after the break.