Jordan Spieth fired a stunning 63 to take a one-shot lead into the weekend at the halfway stage of the Farmers Insurance Open at Torrey Pines.

The American took advantage of playing the easier North Course as he recorded nine birdies to finish the day on 10 under, one shot clear of overnight leader Stewart Cink.

Cink, playing the tougher South Course, recorded a one-under par 71 with Nicolas Colsaerts a shot further back after recording an impressive 67 over the same terrain.

Spieth began his round on the back nine and opened with a birdie before picking up further shots on 13,14 and 18.

Five birdies in seven holes from the second to the eighth then saw the 20-year-old come home in five under and open up a narrow advantage over the rest of the field.

"I've been feeling great since I got here," he told "I'm striking the ball really well."

Spieth was playing in a group alongside defending champion Tiger Woods and the world number one endured a frustrating day as he fired a 71 to sit one under.

Playing his first tournament of 2014, Woods failed to make the most of his respectable level-par round on the South Course on Thursday as he fired two birdies and a bogey to make the cut by just a single stroke.

"I wouldn't say (my game is) rusty," he said. "It was just a fraction off and, you know, at this level and on golf courses like this, if you're just a fraction off it doesn't take much."

Cink is searching for his first victory since winning the Open Championship at Turnberry in 2009 and was going well at two under for the day through 10 holes.

Two bogeys then saw him slip back into the pack but a birdie on his final hole of the day put the 40-year-old out on his own in second.

Colsaerts' bogey-free 67 was the best round of the day on the South Course and the big-hitting Belgian believes the Torrey Pines lay-out is ideal for his style.

"I think it suits my game pretty good," he told Sky Sports 4. "It's a long ball-park. If you get the right shots into greens (it is a) US Open-type set-up. I like it."

Australian Marc Leishman and American Billy Horschel shared fourth-place on seven under and were followed by a group of five players a further shot back including Scotsman Russell Knox.

Jason Day was then in the group at five under after shooting a 73 while another Scot, Martin Laird, was another shot back.

Lee Westwood and Keegan Bradley were amongst those at three under while Phil Mickelson, who was struggling with a back problem, was on two under alongside European Ryder Cup hero Ian Poulter.