Phil Mickelson bogeys Nos. 8 and 9 to drop out of the lead he had held since the first round.
Bill Haas shot a 2-under 33 on the front nine and added a birdie on the short, par-4 10th to move into sole possession of first at 8 under.
Mickelson, Jonathan Byrd and Keegan Bradley are tied for second. Bradley birdied Nos. 7 and 9 to offset some early bogeys and get back to even par for his round.