SAN ANTONIO, 28 Mar 2015 (AFP) - Walker's six-under-par total of 138 put him one in front of overnight leader Charley Hoffman, who posted an even-par 72 and was joined on 139 by Australian Aaron Baddeley, who shot a 71.
It was a further stroke back to another Texan, Jordan Spieth, who carded a 69 and was tied on 140 with Kevin Na, who shot a 68.
Walker, pleased to be playing in front of family and friends, took advantage of improved weather to grab two birdies in his first five holes before his only bogey of the day, at the par-four 17th.
He responded with a birdie at 18, and closed strong with three birdies on the trot at six, seven and eight -- a run that included a 19-foot birdie putt at the par-three seventh.
"I was just kind of around the hole, didn't make anything, and then finally got one to go on six," Walker said.
"I hit a good iron shot, just got it on top of the ridge there on seven and made that putt.
"And that 12-footer I made for birdie on the par-five (the eighth), that was a nice little finish," added Walker, who is seeking his second title of the season after his win in the Sony Open.
The late burst let Walker overtake Hoffman, who was three-under for the day through his first nine holes but had three bogeys coming in to fade.
Baddeley also teed off on 10 and shook off a double-bogey at the par-four 15th, making five birdies and two bogeys the rest of the way.
Walker said a win at TPC San Antonio would be special.
"A win anywhere means a lot," he said. "But being at home, you get to have parents, in-laws, friends, best friends, distant family. It would be cool. It doesn't put anymore pressure on you, I think. If anything you've got a nice support crew out there and you've got good vibes and good mojo — and I believe in all that stuff."
Walker's fellow Texan, Spieth arrived in San Antonio off a dramatic playoff victory in the Valspar Championship in Florida -- his third victory in five months.
For Na, TPC San Antonio will always be linked to the 16 he recorded on the par-four ninth in 2011, but he's hoping to add some new, better memories to his history here.
"I really like this course and played well today," Na said.
Five-time major winner Phil Mickelson, tuning up for the first major of the year at the Masters in a fortnight, fired an even-par 72 to head a group on 142.
He was joined by another former Masters champion in Zach Johnson along with Brendan Steele, Chris Kirk and Billy Horschel.
Leading second-round scores on Friday in the US PGA Tour $6.2 million Texas Open (USA unless noted, par-72):
138 - Jimmy Walker 71-67
139 - Aaron Baddeley (AUS) 68-71, Charley Hoffman 67-72
140 - Kevin Na 72-68, Jordan Spieth 71-69
142 - Brendan Steele 74-68, Chris Kirk 71-71, Billy Horschel 72-70, Zach Johnson 71-71, Phil Mickelson 70-72
143 - Cameron Beckman 71-72, Brendon Todd 73-70, Chesson Hadley 71-72, Jason Kokrak 72-71
144 - Daniel Summerhays 71-73, John Merrick 72-72, George McNeill 74-70
145 - Jeff Overton 75-70, K.J. Choi (KOR) 75-70, Ryan Palmer 70-75, John Huh 73-72, Kyle Reifers 77-68, Scott Pinckney 73-72, Robert Garrigus 75-70, David Lingmerth (SWE) 74-71