Top-four duo Jason Day and Rickie Fowler were among those to miss the cut at the Farmers Insurance Open.
Anyone not under par after two rounds at Torrey Pines was cut from the field and Fowler, who won last week in Abu Dhabi on the European Tour, missed out by one shot after bogeying the 17th on the South Course.
Defending champion and world number two Day shot a two-over-par 74 to miss the cut, while another top-10 player in England's Justin Rose also failed to make the weekend.
At the top of the leaderboard, the halfway lead is shared at nine-under by Gary Woodland and KJ Choi.
Woodland hit a five-under 67 on the South Course and Choi equalled that score on the North Course to lead by one stroke from Dustin Johnson.
