LA JOLLA, January 25, 2014 (AFP) - 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.
Leading second-round scores on Friday in the $6.1 million US PGA Farmers Insurance Open (USA unless noted):
134 - Jordan Spieth 71-63
135 - Stewart Cink 64-71
136 - Nicolas Colsaerts (BEL) 69-67
137 - Billy Horschel 70-67, Marc Leishman (AUS) 66-71
138 - Morgan Hoffmann 72-66, Gary Woodland 65-73, Russell Knox (GBR) 71-67, Pat Perez 67-71, Erik Compton 69-69
139 - Brad Fritsch (CAN) 69-70, J.B. Holmes 71-68, Kevin Tway 69-70, Justin Hicks 71-68, Charley Hoffman 69-70, Scott Stallings 72-67, Jason Day (AUS) 66-73, Kevin Chappell 73-66, Jamie Lovemark
140 - Martin Laird (GBR) 69-71, Matt Jones (AUS) 75-65