Walker seizes PGA lead of just one stroke over Simpson
Walker stood on 12-under 128 through 36 holes, one stroke ahead of reigning US Open champion Webb Simpson of the United States, the defending tournament champion who fired a 63.
Spain's Sergio Garcia, Sweden's Carl Pettersson, American Harrison English and South Africa's Tim Clark shared third on 130 but players were scattered across the course, all with six holes or fewer to complete.
Walker birdied the second and third holes and closed the front nine with back-to-back birdies as well. He birdied the 11th and then charged in with birdies at the par-5 15th, par-3 16th and par-4 17th to grab the lead.
"It was pretty boring-looking golf -- not a lot of drivers, not a lot of 3-woods," Walker said. "There's a lot of 5-woods and some irons, and it's just kind of placement around the golf course."
Walker, 33, is seeking his first PGA title. He had three top-10 finishes in his first six tournaments of the season but suffered a left knee injury and skipped the US Open for treatment on the injury.
He snatched the top spot from Simpson, who closed with four birdies in the final five holes in his own charge up the leaderboard.
"To play a round on a golf course this tricky without a bogey is always a good thing," Simpson said.
Pettersson, who led after an opening-round 62, birdied the par-5 15th in a two-under 68 second round to stumble back.
"I struggled. Didn't have much, but I thought it was a good comeback," said Pettersson. "Two-under par was OK for the game that I had, and hopefully I can hit the ball better on the weekend and have a chance."
American Tim Herron matched the tournament record with a 61 but was seven strokes off the pace.
"I didn't really have anything to lose," Herron said. "I kind of zoned in a little bit today and just kind of kept rolling and making putts."
Herron hopes to advance at least eight spots on the points list to crack the top 125 and qualify for the PGA playoffs that begin next week at The Barclays.
Among those missing the cut and on the bubble for reaching the field next week were American Boo Weekley, rated 121st on the points list, and No. 125 Jhonattan Vegas of Venezuela.