Bryn Parry, Jeff Wood and Franklin Langham had 5-under 67s to share third place. Eight players were tied one stroke further back at 68.
Letzig, a rookie, hasn't made a bogey since the 12th hole of the first round at last week's Knoxville Open, where he finished third. It was his third top-10 finish of the season.
'It's scary. I hope I make a bogey soon,' he said.
Thursday, Letzig hit 12-of-14 fairways to lead the field and reached 16 greens in regulation, second among the 155 players. He needed just 29 putts in a bogey-free round.
'I played really solid,' he said. 'I had a good game plan where I wanted to play very conservative off every tee. I wanted to hit the least amount of club I could hit off the tee and still get away with it. That was one of the best rounds of golf I've played all year.'
Claxton won earlier this season at the Melwood Prince George's County Open and ranks third on the Nationwide Tour money list. He owns five top-25 finishes this year.
In the first round, he made his only bogey at the par-3 12th -- his third hole. He came back with three consecutive birdies from the 15th, then made three more birdies on the front nine.
Midway through the season, the Nationwide Tour veteran is all but guaranteed a top-25 finish on the money list and a PGA TOUR card next season.
'It frees you up a bit when you know you are playing well,' said Claxton. 'When you are swinging good and feeling good you don't let the bad shots bother you. I think that's the 'zone' that guys talk about.'
Joe Daley, Jimmy Walker, Chris Smith, Tjaart van der Walt, Danny Briggs, Bill Glasson, Jon Mills and Brian Quackenbush share sixth place at 4-under 68.