|CareerBuilder Challenge first-round leaderboard|
|-15 J Dufner (US); -14 J Lovemark (US); -12 A Lahiri (Ind), A Hadwin (Can) J Gore, A Loupe (US) Selected others: -11 P Mickelson (US); -7 M Laird (Sco); -5 L Donald (Eng)|
American Jason Dufner scored a seven-under par 65 to open a one-shot lead after the second round of the CareerBuilder Challenge in California.
The 38-year-old hit eight birdies to move one stroke clear of compatriot Jamie Lovemark, who also carded 65.
Defending champion Bill Haas scored a second straight 66 to share third.
Haas is joined by overnight co-leader Anirban Lahiri of India, who shot 68, Canada's Adam Hadwin and fellow Americans Jason Gore and Andrew Loupe.
Another stroke back was five-times major winner Phil Mickelson, who said he was nearing top form after returning a 65.
"I'm probably a week away," he said. "But I've also won with a lot less game than I have right now, so I still expect to get in contention and have a good weekend."
Scotland's Martin Laird is the highest-placed Briton, eight shots off the lead and tied for 35th, while England's Luke Donald is two strokes further back.