(Adds headline. No change to copy.) By Ben Everill LA JOLLA, California, Jan 30 (Reuters) - American Scott Brown and South Korean K.J. Choi share the lead after the third round of the Farmers Insurance Open on Saturday. Choi birdied the par-five 18th to shoot even-par 72 and join Brown (70) at nine-under-207, one shot ahead of Jimmy Walker and Gary Woodland at Torrey Pines in southern California. Choi, winless on the PGA Tour since 2011, is chasing his ninth tour title, while Brown has one career win. Twenty-three players are bunched within four shots on a packed leaderboard. ... More...