Nicholas Thompson holds a one-shot lead over fellow American Michael Thompson entering Friday's second round of the $6.3 million Farmers Insurance Open at Torrey Pines Golf Course.
Nicholas Thompson fired an eight-under-par 64 on the North Course, with an eagle on the first hole, seven birdies and a bogey on the 11th. He said he is looking forward to playing the South Course Friday, which he called one of his favorite courses.
"It is a great test from tee to green and I always look forward to it," said Nicholas Thompson, a brother of LPGA star Lexi Thompson.
"Over my career here, the North Course has been my falter in relationship to the field. I usually play the South Course well. It fits my eye really good and I like a lot of the golf shots."
Nicholas Thompson has never won on the PGA Tour. His best finish was tying for second place in the 2008 Ginn sur Mer Classic, a now-defunct Fall Series event. He tied for third at last year's Crowne Plaza Invitational at Colonial.
Michael Thompson, who is not related to Nicholas Thompson, finished his round of seven-under-par 65 with back-to-back birdies.
Brooks Koepka and Cameron Tringale are tied for third at six-under-par 66, two shots behind Nicholas Thompson.
Each of Thursday's four lowest scores came on the North Course. Jhonattan Vegas had the low score on the South Course, a five-under-par 67, putting him in a five-way tie for fifth, three shots off the lead.
Tiger Woods withdrew because of pain in his back after playing 11 holes at two-over-par. Woods said he began feeling back pain when he was standing on the putting green during a fog-caused suspension in play and "it just never loosened back up again."
"When we went back out, it just got progressively tighter," said Woods, who has won the tournament a record seven times, most recently in 2013.
Woods said the pain was the result of "my glutes are shutting off."
"I tried to activate my glutes as best I could, in between (the suspensions of play), but they never stayed activated," said Woods, who was coming off his worst round as a professional, an 11-over-par 82 at the TPC Scottsdale course a week ago Friday, causing him to miss the cut at the Waste Management Phoenix Open.
San Diego native Phil Mickelson was unable to complete his round on the South Course Thursday because of fog delays, shooting a one-over-par for 15 holes when play was stopped because of darkness.
The field of 156 will be reduced to the low 70 and ties following the conclusion of Friday's round.
The tournament will conclude with rounds on the South Course Saturday and Sunday. The winner will receive $1.134 million.
