Tiger Woods limped out of the US PGA Tour event at Torrey Pines after 11 holes on Thursday as back trouble left him well off the pace set by Nicholas Thompson.

Thompson fired an eight-under par 64 for the clubhouse lead in the fog-disrupted round, which was halted by darkness with 42 players still on the course.

By the time play was halted, 14-time major champion Woods was long gone.

The 39-year-old superstar could be seen grimacing and rubbing his back during the round and was two-over for the day when he spoke to his playing partners on the Torrey Pines North Course and walked gingerly away, eventually being taken off in a golf cart.

In a brief word with reporters, 39-year-old Woods said his lower back got tight during one of two fog delays that held up play for a total of more than two hours on Thursday morning.

"I just never loosened back up again," he said in a brief interview in the parking lot. "And when we went back out it just got progressively worse."

Woods' early departure follows his career-worst 82 in the second round last week at Phoenix, where he missed the cut by 12 strokes.

Woods, chasing the record 18 major titles won by Jack Nicklaus, said in Arizona that he was not injured and just needed more tournament work to try to recover his lost form.

He was no doubt hoping to get that at Torrey Pines, where his eight titles include his most recent major triumph, at the 2008 US Open.

Instead Woods, who has fallen to 56th in the world, endured yet another setback.

"It's frustrating that it started shutting down like that," Woods said. "I was ready to go. I had a good warmup session the first time around, and I stood out here and got cold and it started deactivating again."

Woods said the pain was "different" from the back pain he dealt with early last year, when he opted for surgery on March 31 to ease a pinched nerve and missed the Masters and US Open while recovering.

Overall in six PGA Tour events since he returned to competition at the PGA Tour's National, Woods has missed three cuts -- including at the 2014 PGA Championship, withdrawn twice and finished 69th at the British Open.

Thompson seeks first title

Thompson, seeking his first PGA Tour title, is coming off a missed cut in Phoenix.

He had a one-stroke lead over Michael Thompson, while Brooks Koepka, the winner in Phoenix, opened with a six-under 66 to share third place with Cameron Tringale.

It was a further stroke back to England's Ian Poulter, Chad Campbell, Sweden's Freddie Jacobson, Venezuelan Jhonattan Vegas, Zimbabwe's Brendon de Jonge and Chris Kirk on 67.

Phil Mickelson, a three-time winner of the tournament, was at one-over par through 15 holes when play was halted.

Dustin Johnson, who was making his first tour start since last year's Canadian Open was two-over with one to play on Torrey's South Course, the more difficult of two layouts in use over the first two rounds.