Tom Jenkins fired a 67 to join Des Smyth in a tie for third place at 7-under-par 137. Mark McNulty and Leonard Thompson followed at 6-under-par 210.
Levi began his move with back-to-back birdies from the par-5 fourth at The Westin Savannah Harbor Resort and Spa. Levi then birdied the par-5 seventh and added a birdie at the par-3 eighth.
The 53-year-old hit his drive in the rough at the par-4 12th, but played his second shot within 3 feet of the hole. Levi converted the short birdie putt and missed the green to the left at the par-5 13th.
Levi pitched to 3 feet and rolled in the birdie try to move to 11 under. He had another birdie chance at the 14th, but failed to convert from 6 feet out.
Levi then found trouble down the stretch with a bogey at the par-3 17th and another at the last to secure a slim lead with one round to play.
'I've been playing well the entire year, I just haven't won yet,' Levi said. 'I am starting to putt better which helps. I made a good bogey at 18. I had a plugged lie and really had no shot. I could have had a pretty good lead, but it was a tough day.'
Purtzer had a strong start with a birdie at the par-4 first and he added a birdie at the par-5 seventh to climb to 9 under.
The hard-hitting 53-year-old then reached the green in two at the par-5 11th, but left his eagle try short. Purtzer tapped in for a birdie to move to 10 under, but he stumbled coming in under windy conditions.
Purtzer's chip shot at the par-4 14th fell short in a bunker and he walked away with a bogey. He dropped another shot at the par-4 16th to finish one shot back.
'The wind blew harder the last hour and a half. It was just a tough day,' said Purtzer. 'The pins were in some tough spots too. I didn't play as good the last five holes.'
Craig Stadler, Bob Gilder, Dana Quigley, Gil Morgan, Jim Thorpe and J.C. Snead share seventh place at 5-under-par 139.
Jay Haas, Jim Dent, Bruce Fleisher and D.A. Weibring are one shot further back at 4-under-par 140.