Billy Horschel, uncertain of playing from back stiffness, opened the Farmers Insurance Open with¬†the low score of 63, -9, on a rare Wednesday start at the North Course, Torrey Pines in La Jolla, Calif. Michael Thompson is in second at 8-under; while Kevin Tway and Stephan Jaeger,¬†Germany, finished third with 7-under. The leaders took advantage…