Harris English fired a 64 to lead at the halfway stage of the Farmers Insurance Open at Torrey Pines.
After carding a four-under-par 66 on the South Course on Thursday, English continued his good form on the North Course with birdies at the first, seventh and ninth holes to reach the turn in 33.
The 25-year-old picked further strokes at the 10th and 14th before an impressive iron shot at 17 set up his sixth birdie of the round to leave English at 10-under-par.
Nick Watney moved into a three-way tie with Jhonattan Vegas and Scotland's Martin Laird for second place following an error-free 65 on the North Course and trails English by two shots.
First-round leader Nicholas Thompson slipped into fifth place on the leaderboard after carding a one-over-par 73.
