Bohn made six birdies and had one bogey at the Quail Hollow Country Club course for a 36-hole total of 135.
Anthony Kim, who challenged for a win two weeks ago at the Heritage on Hilton Head Island, was alone in second at 137 after also firing a 67. Former champion Jim Furyk, George McNeill and Dudley Hart shared third at 138 while Camilo Villegas and Heath Slocum were at 139.
Phil Mickelson suffered two late double bogeys and fell seven shots off the pace.
Bohn began this year playing on a major medical exemption after missing the last six months of 2007 due to a rib injury. By finishing sixth and winning $198,000 at the Heritage, he earned enough money to be granted a medical extension for the remainder of this season.
"I'm totally freed up," Bohn said. "It was a big thing to make sure I got my medical situation taken care of and another huge thing to play in the Players Championship (next week)."