Rick Price, Tee McCabe and Ron Whittaker are knotted in fourth place at minus- six at the TPC at Wakefield Plantation.
Carter collected his first birdie of the round at the par-4 second when his 15-footer found the bottom of the cup. He added another birdie at the fourth from 8 feet, then caught a little fire later in his opening nine.
At the par-5 sixth, Carter missed the green with his second shot, but chipped to 8 feet. He rolled in the birdie putt and made it two in a row when his 9-iron tee ball stopped 10 feet from the stick at seven.
Things went downhill quickly for Carter. He failed to get up and down from a bunker for par at the eighth, then drove into a hazard at the ninth. That led to another bogey and he made the turn at 2-under 33.
Carter parred his first three holes on the back side, then rattled off three birdies in a row from the 13th, all from the 6-foot range. He tapped in a short birdie putt at the 17th and reached 7under par with a 5-foot birdie putt on the par-5 last.
'I made everything today,' admitted Carter, who won three times in 2003, but has struggled since. 'Today was one of those days where everything clicked for me. This type of round is definitely a confidence builder.'
Thompson started on the back nine Thursday and promptly birdied the 10th. He added birdies at the 12th, 14th and 18th to make the turn at 5 under par.
He flew out of the gate on the second nine with a birdie at the first and a 40-foot birdie putt at the second. Thompson birdied the seventh, bogeyed eight and birdied nine to join Carter in the lead.
'It was one of those days,' said Thompson. 'It was a really easy 7 under. I never really struggled for any pars. I hit it good and putted good. I hit a lot of greens and fairways and made a lot of putts in the 10-15-foot range.'
Letzig was the only one of the co-leaders to tee off in the afternoon and tallied his first birdie at the par-4 fourth. He collected back-to-back birdies at nine and 10, then finished strong.
He birdied 13 and 14 to get to 5 under par for the championship. Letzig, currently 20th on the Nationwide Tour money list, birdied 16 and 18 to join the group in first.
Scott Gump, Elliot Gealy and Jon Turcott are tied in seventh place at 5-under-par 66. Phil Tataurangi, Mario Tiziani, Marc Turnesa, Kris Blanks, Brett Bingham and Tony Parrish share 10th place at minus-4.
Brenden Pappas has a chance to become the first player in Nationwide Tour history to successfully defend a title. He started off in decent shape with a 1-under-par 70 and is tied for 43rd place.