Sergio Garcia, playing for the first time since going 4-0-1 in the Ryder Cup two weeks ago, bogeyed the 18th hole to shoot a 5-under 67. He was joined in a tie for second by Ryder Cup teammates Luke Donald and Miguel Angel Jimenez, Stuart Appleby, Adam Scott and Steve Flesch.
Tiger Woods teed it up on Thursday despite a back injury that had him contemplating withdrawal. He grimaced and groaned his way to a 4-under 68 and a share of eighth place.
Woods slept awkwardly on his plane last week and tweaked the area between his shoulder blades. He said on Wednesday that it would be a tee-time decision and ultimately decided to give it a go.
'I thought it might loosen up a little bit, but it didn't,' said Woods, the two-time defending champion. 'I was hoping the spasms would go away, but that didn't happen, either. I just had to get through it somehow and post a number.'
Woods looked to be in pain off the first tee, but played surprisingly well. He birdied his first two holes, before collecting five consecutive pars at Mount Juliet Conrad.
He sank a 25-footer for birdie at the eighth, then made a 30-footer for birdie at the next to make the turn at 4-under-par 32. Woods birdied the 11th, but made a mess of No. 12. His second buried in a greenside bunker, then he blasted out to a trap on the other side of the putting surface. Woods could do no better than bogey to fall to minus-4.
The No. 2 player in the world recorded another birdie at the 17th to get to 5 under, but trouble loomed at the difficult closing hole. Woods drove into the right rough and took a hard swing at his second. The impact caused Woods to nearly fall to his knees, while shouting in pain.
Woods could not save par from 20 feet but is still in the hunt for his first stroke-play victory since this tournament in 2003.
'I figured if I could just get the ball on the green somehow, I've been putting great, it's just a matter of getting on the green and making putts,' said Woods. 'I was hoping I could get there in regulation and I did that most of the day and made a lot of putts.'
Woods was joined in eighth at 4 under by U.S. Open champion Retief Goosen, Zach Johnson, Thomas Bjorn, Nick O'Hern, Lee Westwood, Robert Allenby and Justin Leonard.
After the drama of whether Woods would tee it up or not was answered, the focus shifted to Hamilton, who is virtually a shoo-in for PGA Tour Rookie of the Year after his win at Royal Troon and a title at the Honda Classic.
Hamilton parred the first, then hit a poor pitching-wedge at No. 2 that barely carried the greenside bunker. He rolled in the 20-footer for birdie and made it two in a row with a 12-foot putt at the par-3 third.
He laid up short of the green with his second at the par-5 eighth hole. Hamilton had 70 yards to the hole and hit a lob-wedge to 6 feet for his third. He drained the putt to reach 3 under for the championship.
It was a run of golf late on the back nine that vaulted Hamilton into the lead. At the par-3 14th, Hamilton hit a 6-iron to 12 feet to set up birdie. He made it back-to-back birdies with a 25-footer at the 15th and polished off three birdies in a row with a crazy birdie at the 16th.
Hamilton drove left over tents at the 16th, but had a good lie and good angle at the flag. He had 110 yards and hit a sand-wedge to 15 feet to set up his sixth birdie of the round. Hamilton two-putted from 50 feet at 17 for his fourth birdie in as many holes.
Even though play was contested under lift, clean and place on Thursday, Hamilton was not immune from mistakes. He missed the fairway at the 18th and missed the green with his second. Hamilton's third landed 40 feet short of the hole and his par-saving putt missed 4 feet past. He made that putt for a 66, but still held first by himself.
'The last hole is probably going to be played as the toughest one for the whole day, if not the whole tournament,' said Hamilton. 'At least I bogeyed a hard hole instead of an easy one.
'The putter felt good the whole day. If you can't putt on these greens, you can't putt, because the greens are spectacular. You may not be able to hit it close to the hole but it's going to stay on the green.'
Garcia was the player closest to matching Hamilton in the lead on Thursday. The Spaniard was 6 under through his first 10 holes, but cooled at the 14th when his 5-iron approach landed left of the green. Garcia made bogey there but got back to 6 under with a 35-foot birdie putt at the 16th.
Garcia drove into the rough at 18 and tried to get a 3-wood on with his second shot. The ball landed in a greenside bunker and he could not get up and down for par.
'It was a pretty simple 5 under,' said Garcia. 'I bogeyed the last, but I hit my worst drive all day. I managed to make a couple on the front nine, and unfortunately didn't make as many on the back, but it was good to play that consistent all day long.'
Ernie Els and local favorite Padraig Harrington are part of a group tied for 16th at 3-under-par 69. Paul McGinley, another Irishman, carded a 2-under 70 on Thursday.