Walker is bidding for his third top-five finish at the Classic, after a pair of fourth-place finishes in 2010 and 2011. He thundered down the stretch with five birdies on the back nine for his own 64 Saturday. His score is the best of 14 players who have broken the par-70 in all three rounds.
"I like the tee shots, like the second shots and feel comfortable," he said. "There's a couple of places on Tour I feel really comfortable and seem to play well."
Swedish native Jonas Blixt, a Florida State graduate and 2012 event winner, sneaked into third place at 10 under with his second straight 67. He suffered a double-bogey at No. 13 but picked those strokes back up with birdies at Nos. 15 and 17.
Matt Jones, 19-year-old Jordan Speith and Steven Bowditch are tied for fourth at 9 under. Jones has rattled off 11 birdies in 24 holes after he was headed for missing the cut.
Spieth, the special temporary Tour member, needs a victory to join the FedExCup playoffs. He knows he needs a lower score to do it.
"[I need to] have a better start today," Spieth said. "Looks like another 67 probably won't cut it, so I'm going to have to shoot a really low round and that's saying a lot. The greens are firming up big-time and it's making some of these pins more inaccessible."
Six players are tied at 8 under: Pat Perez, Bill Haas, Rory Sabbatini, D.H. Lee, Tag Ridings and Tommy Gainey. Perez had the best round of the bunch with a 66, including an eagle at the par-5 12th.
Gary Woodland was the first of three players to post a 64 and came off the 1-under cut line to join a three-way tie at 7 under. Former Classic champions Scott Stallings and Ted Potter Jr. are part of an 11-way tie for 16th.
Matt Every, the second-round leader at 9 under, tumbled to a tie for 27th with a 4-over 74. He suffered four bogeys on the front nine and consecutive double-bogeys on the 13th and 14th.
Tom Watson, the 63-year-old Greenbrier pro emeritus, shot a 72 to slip to a tie for 62nd. He avoided the secondary "MDF" cut, which clipped 10 players for today's final round.
That will begin today with Martin Flores at 8:30 a.m. Wagner and Walker tee it up at 2 p.m.
"In Houston, when I won in 2008, I was really nervous," Wagner said. "I don't know how I managed to close that one out. I was shaking, felt sick all morning.
"It got a little easier in Mayakoba when I won in 2011, still very nervous. At Sony [2012 in Hawaii], it was a weird feeling; I felt pretty comfortable after the first few holes.
"Hopefully - I mean, last group on Sunday, you're always going to be nervous, but I'm sure I'll be OK."
Reach Doug Smock at 304-348-5140, dougsm...@wvgazette.com or follow him at twitter.com/dougsmock.