SAN DIEGO — Top-ranked Jon Rahm closed with an eagle on the tougher South Course at Torrey Pines for a 6-under 66 on Wednesday, trailing leader Billy Horschel by three strokes after the first round of the Farmers Insurance Open.

Horschel shot a bogey-free 9-under 63 on the North Course and led Michael Thompson by one stroke. Of the 30 players who shot 67 or better, 26 played the North. Rahm’s was the best score on the South by one over Luke List, Peter Malnati and Cameron Tringale. The players switch courses Thursday and play the final two rounds on the South.