John Mallinger's Frys.com Open lead was reduced to only two strokes after a one-under 70 took the American to 15 under in California.
Mallinger, four ahead overnight, carded eight shots worse than his course record-equalling 62 a day earlier.
In-form Swede Jonas Blixt reduced the gap at the top of the leaderboard thanks to a five-under 66 that left him on 13 under.
"I just didn't have it all today," Mallinger said. "I didn't drive it as well as I did yesterday. I think I hit every fairway yesterday, and then today I just got off to a weird start.
"But I hung around there and made some birdies on the back nine that got me back into position. Still got the lead, still got a good spot, and looking forward to tomorrow."
Charles Howell III (66) and Jason Kokrak (67) are one shot behind Blixt and three off the lead while Brazil's Alexandre Rocha was joined by veteran Fijian Vijay Singh on 11 under after 66s.
Russell Knox of Scotland had an excellent day after a six-under 65 took him to 10 under par with a round to play, and England's Greg Owen was on the same score after his 68.
Mallinger has vowed to remain on the attack on the final day, expecting plenty of players to make a run with low rounds.
"I'm going to still stay aggressive and try to make as many birdies as possible," he said.
"It's going to be a birdie day. If I can go out and shoot three or four under, then we will see if those guys can catch me."