Napa - Brendan Steele fired a three-under par 69 on Saturday and will take a one-shot lead into the final round of the Frys.com Open in search of a wire-to-wire win.
Steele, seeking a second US PGA Tour title, has led since a nine-under par 63 in the opening round.
His three-under effort gave him a 14-under par total of 202, one shot in front of a pair of surging players - Web.com tour graduate Andrew Loupe who carded a 63 and Kevin Na, who posted a 64 on the Silverado Country Club course.
Loupe, who won the penultimate event in the web.com finals series in September to secure his US tour card, opened the third round with five birdies in a row.
He birdied 14-17 before capping his round with a par.
"I felt like I was swinging pretty freely today," said Loupe, adding that his plan for Sunday was to try to "keep that mojo and positive energy going".
Na, whose only PGA Tour victory came in 2011, played without a bogey, and drained a seven-foot eagle putt at the 16th. After four birdies on the front nine, he also birdied 15 and 18.
England's Justin Rose carded a 68 and was two shots off the pace in a group of eight players on 204.
He was joined by Argentinian rookie Emiliano Grillo (65), Jason Bohn (64), Kyle Reifers (65), Canadian Graham DeLaet (69), Harold Varner (69), Venezuela's Jhonattan Vegas (69) and Will Wilcox (69).
World number three Rory McIlroy of Northern Ireland struggled with his putter for the third straight day.
His 71 left him eight shots adrift in a tie for 39th.
"Not to be able to break 70 today is quite disappointing," said McIlroy, whose only two birdies came at par-fives on which he missed eagle attempts.
"I think it's more mental than anything else," McIlroy said. "Whenever you don't see anything go in, it makes it harder and harder each and every hole that goes by."
McIlroy also endured a scary moment when, having just chipped on the 17th green, a drive by Grillo narrowly missed hitting him.
The with the par-four playing at 296, Grillo opted to go for the green, and thought McIlroy and the others in his group were out of the way.
"I heard that I almost hit him, but I really apologize," he said.
McIlroy made light of it.
"Missed me by a couple of inches," the four-time major champion said. "Would've put me out of my misery, to be honest with you."
Leading third-round scores on Saturday in the $6 million USPGA Tour Frys.com Open (USA unless noted, par 72):
202 - Brendan Steele 63-70-69
203 - Andrew Loupe 68-72-63, Kevin Na 68-71-64
- Jason Bohn 72-68-64, Kyle Reifers 68-71-65, Emiliano Grillo (ARG)
68-71-65, Justin Rose (ENG) 67-69-68, Harold Varner 65-70-69, Graham
DeLaet (CAN) 67-68-69, Will Wilcox 68-67-69, Jhonattan Vegas (VEN)
205 - Justin Thomas 66-70-69
206 - Jamie Lovemark 70-71-65, Tyrone Van Aswegen (RSA) 69-68-69, Charles Howell 69-69-68, Patrick Rodgers 68-69-69
207 - Brooks Koepka 69-72-66, Luke Guthrie 71-70-66, Sean O'Hair 68-71-68
- Hudson Swafford 69-72-67, Miguel Angel Carballo (ARG) 72-69-67, Ben
Crane 69-71-68, James Hahn 74-66-68, Charl Schwartzel (RSA) 71-68-69,
Russell Henley 67-69-72, Lucas Glover 69-73-66