Spieth storms into Torrey Pines lead
Jason Wagner hits out of the bunker on the 9th hole during the second round of the Farmers Insurance Open at Torrey Pines South Course on January 24, 2014 in La Jolla, California - by Donald Miralle
Spieth was partnered with Tiger Woods, but he blew away the defending champ and seven-time tournament champion, who was nine shots off the pace after shooting a one-under 71.
The 20-year-old Spieth, who was three years old when Woods won his first Masters, finished his first two rounds at 10-under par 134.
Former British Open champion Stewart Cink fired a one-under 71. He was the first-round leader, but dipped into second place at nine-under.
Woods finished his two rounds tied for 50th at one-under-par 143.
"I was a foot off all day," said Woods. "It was one of those frustrating rounds. When I had opportunities to get something going I stubbed my foot.
"Today with the way things were going I thought to get to within five would be fine. But we've got long way to go."
Nicolas Colsaerts carded a five-under 67 on the more difficult South Course at Torrey Pines as the Belgian vaulted into third place at eight-under-par 136.
Billy Horschel had a 67 on the North Course and that helped him move into a share of fourth at seven-under. He was joined there by Aussie Marc Leishman, who posted a one-under 71 on Friday.
Gary Woodland (73), Pat Perez (71), Erik Compton (69), Russell Knox (67) and Morgan Hoffmann (66) are all tied for sixth place at six-under-par 138.
Former two-time winner Phil Mickelson stumbled to a one-over 73. He was tied for 32nd at two-under.