Sea Island, GA (My Sportsbook) - Michael Thompson posted a three-under 67 on Saturday to move to the top of the leaderboard after the third round of the McGladrey Classic.

Thompson, a PGA Tour rookie, finished 54 holes at 13-under 197 and is one stroke ahead of second-round leader Billy Horschel, who struggled late en route to an even-par 70 at the Seaside Course at Sea Island Resort.

Webb Simpson's quest for getting to first on the PGA Tour money list is in great shape, but now he can concentrate on becoming a three-time winner this year.

"The only goal for today was keep myself in the golf tournament and try to have a chance to win tomorrow, and I think we did that," he said.

Simpson, who trails Luke Donald by almost $69,000 for the top spot on the money list with just one tournament left next week, managed a one-under 69 and is tied for third place with former Masters champion Trevor Immelman, who fired an eight-under 62 on Saturday. The pair came in at 11-under 199.

Immelman has been hampered by a wrist injury since his breakthrough at Augusta in 2008. He hasn't even posted a top-10 finish since the 2008 Tour Championship, but feels healthy enough to get back into the winner's circle.

"It's been giving me a lot peace of mind to be able to go out and practice when I want to practice and as much as I want to practice, work on the things that I used to be able to without being any pain," said Immelman. "And so with all that work I started to see some better signs; as I seen better signs I got a bit more confidence; and so it's really just that type of a process."

Jeff Overton (66), Kris Blanks (66), Nick O'Hern (69) and 2010 British Open champion Louis Oosthuizen (69) are knotted in fifth place at nine-under-par 201.

Everyone will be chasing a winless tour rookie on Sunday.

Thompson trailed Horschel by two strokes at the start of the third round and Horschel distanced himself a bit with a seven-foot birdie putt at the first hole.

Both Thompson and Horschel birdied No. 2, but Thompson got within two thanks to a 14-foot birdie putt at the par-three sixth. He closed the gap further with a nine-footer for birdie at the ninth.

Horschel made routine pars, but Thompson made some amazing ones just to keep pace.

At the par-three 12th, Thompson missed the green right and pitched to eight feet. He holed the clutch par save to stay one behind, but that par seemed downright routine compared to the one he made at the 14th.

Thompson drove into a small bunker on the left side and he tried to hook his second toward the green but failed. His approach sailed well right of the green. He hit a spectacular pitch to 10 feet and converted the putt for the unlikely par to stay one back.

"Played it like a bunker shot and it came out perfect," Thompson said on television of his third at 14. "Hit a really solid putt and ran away with one there."

Horschel wasn't quite so fortunate at the 16th.

After 13 consecutive pars, Horschel, who showed clear frustration that his putts weren't falling, hit a wild drive into a hazard. He took a penalty stroke and couldn't get his third to the green. Horschel knocked his fourth to 15 feet, but missed the bogey putt and tapped in for double-bogey.

That error cost Horschel the lead and Thompson inched in front by one.

Horschel appeared to be in trouble again at 18 when he pushed his second right of the green. Thompson hit a great four-iron 11 feet short of the flagstick. Horschel chipped to nine feet, and after Thompson missed his birdie putt, Horschel sank his par putt to stay within one.

Thompson will take the lead into Sunday for the first time. His best finish on tour was a fourth at the Transitions Championship and at 116th on the money list, he's safely inside the top 125, but a good finish on Sunday, let alone a win, would guarantee his spot on tour next year.

"Just going to try and hit solid golf shots," Thompson said in his televised interview. "Tomorrow's a new day and I'm going to enjoy it."

NOTES: Thompson was the runner-up at the 2007 U.S. Amateur Championship...Defending champion Heath Slocum shot an even-par 70 and is tied for 33rd at four-under...Paul Casey withdrew on Saturday with a stomach illness, and, at 127th on the money list and not in the field next week, he will lose his PGA Tour card next year...Brian Davis pulled out during the round with a neck injury.