John Mallinger became the second player in as many days to equal the course record at CordeValle and lead the US PGA Tour event in California by four strokes as West Australian Nick O'Hern faltered on Friday.
American Mallinger repeated the first round feat of O'Hern, hitting a nine-under 62, to head the field by four as the 40-year-old Australian slipped down the leaderboard.
Like O'Hern on day one, Mallinger was bogey-free for his round but he also threw in an eagle at the par-five 15th to go with seven birdies, putting him 14 under overall.
That equated to a four-shot lead over compatriot Billy Horschel and Venezuela's Jhonattan Vegas.
O'Hern could only manage a level-par 71, putting him in a share of fourth on nine under alongside Belgian Ryder Cup star Nicolas Colsaerts and Scott Dunlap of the United States.
Dunlap today was eight under, with seven of his eight birdies coming on the back nine as he came home in 29.
Steven Bowditch is the second-best placed Australian at seven-under, seven off the lead, while countryman Matt Jones is a further shot back after shooting a five-under 66.
England's Greg Owen led the British challenge as his two-under round put him seven under overall and in a tie for ninth, three strokes ahead of Scotland's Russell Knox and American defending champion Bryce Molder.
Another Englishman, Brian Davis, scraped into weekend play on one under, making the cut with nothing to spare, but Gary Christian bowed out at the halfway stage.