American John Mallinger, winless in seven years on the PGA Tour, fired a one-under 70 on Saturday to maintain the lead after the third round of the $US5 million the US PGA Tour event in California.
The 33-year-old had a 15-under 198 total at the CordeValle golf course. He equalled the course record 62 in the second round after opening with a 66 on Thursday.
"It was a little scrappy," said Mallinger, who has a two-shot lead. "I didn't have my best off the tee, but I started hitting some good shots coming in. I hit a lot of good putts that just didn't fall.
"Hopefully, I can straighten out the drive and make some putts tomorrow."
Mallinger had finished second twice, including losing in a playoff to Bo Van Pelt three years ago in Milwaukee.
Sweden's Jonas Blixt was second after a 66, while Americans Charles Howell and Jason Kokrak were another stroke back at 12 under. Howell shot a 66, and Kokrak fired a 67.
Australia's Nick O'Hern, who held the outright lead after blasting a course record nine-under 62 in the opening round, posted his second-straight par 71 to slip further down the leaderboard - he is now in a tie for 12th.
Australian trio Nathan Green, Matt Jones and Steven Bowditch are two shots back at seven-under in a share of 28th place.
The 28-year-old Blixt birdied five of the last eight holes. He was even-par on the front nine with a birdie and a bogey.
He shot up the leaderboard with birdies at 11 and 13 and then rolled in a birdie on 15 to get to 11-under.
Blixt birdied the 17th and followed with a six-foot birdie putt at 18 to finish two back. He finished third last week in Las Vegas.
"The front nine is a little harder. The back nine you can make a couple birdies," Blixt said. "Hopefully, I can finish like I did today."
Greg Owen (68), Scott Dunlap (70), Jhonattan Vegas (71), Danny Lee (67) and Russell Knox (65) share seventh at 10-under-par 203.