There were a dozen rounds of 65 or better shot at the Sedgefield Country Club course Friday, including a 61 by Tim Herron that was 15 strokes lower than the score he posted the day before.
Walker, with three Top 10 finishes to his credit this year, completed 36 holes at 12-under 128. U.S. Open champion Webb Simpson fired a 63 Friday to move into second place by himself at 129.
Defending FedEx Cup champion Bill Haas and 2012 U.S. Ryder Cup captain Davis Love were among those in the hunt at 133 -- tied for 11th place. There were 21 players within six shots of the lead heading into the weekend.
Walker lowered his best score of the year by three shots and has yet to bogey a hole in two rounds.
This event is the last chance to qualify for the PGA Tour's four-tournament playoff system, which begins next week. The top 125 point earners in the FedEx Cup points chase will be eligible for the playoff opener.