R3 LEADERBOARD US unless stated -12 S O'Hair -11 T Hamilton -10 D Barron, S Verplank, T Purdy

The 22-year-old sunk four birdies to move to 12 under and nose ahead of Open champion Todd Hamilton, who surged up the leaderboard on Saturday.

Doug Barron, Scott Verplank and Ted Purdy were all tied for third, a stroke further adrift on 10-under.

England's Luke Donald and world number two Vijay Singh are back on six under.

O'Hair is chasing his first victory on the PGA Tour since turning professional at just 17.

But he is trying to take it all in his stride as he attempts to make his narrow lead count on the final day.

"Being in that situation for the first time, I'm pretty happy with the way I handled myself," said O'Hair.

"I think eventually I was going to be in this situation. But this early? I don't think so."

Hamilton, who has had only one top 10 finish since his Open victory over Ernie Els, shot a 65 despite missing two short birdie putts in the final four holes.

Els and Phil Mickelson, world numbers three and four, are in large group of players on five under.

Mickelson made an appalling start to his third round with five bogeys in the first 11 holes but recovered with four birdies in the last six to finish with a level-par 70.

Singh can regain the world number one ranking from Tiger Woods if he comes in the top three on Sunday.