California native John Mallinger equalled the course record of 62 in his home state to take a four-shot lead in the second round of the Frys.com Open.
Mallinger matched the achievement of compatriot Nick O'Hern, who also produced a nine-under par round of 62 the previous day.
O'Hern could only manage a round of 71 and trails Mallinger by five shots at the halfway stage.
Mallinger has been bogey-free in his first two rounds at the CordeValle Golf Club, and produced seven birdies and an eagle to go out to 14-under par overall.
Billy Horschel and Jhonattan Vegas are the closest players to Mallinger back on ten-under, with Ryder Cup star Nicolas Colsaerts the highest placed European a further shot behind.
