Graeme McDowell hit the round of the day to go three shots clear at the World Golf Challenge in California.
McDowell, who was in a chasing pack of three after a first-round 69, signed for a six-under 66 today to move to nine under overall.
He kicked off with three successive birdies and added four more in the back nine to weigh against a solitary dropped shot at the par-four seventh.
American trio Bo Van Pelt, Jim Furyk and Keegan Bradley are tied for second on six under, with the latter making a bogey-free round including three birdies.
Host Tiger Woods lies one stroke further back after signing for a 69 - dropping shots at eight and 15 either side of four birdies in five holes.
Australia's Jason Day is bottom of the 18-man field on two over through 36 holes, with the third and final non-American, England's Ian Poulter, also struggling on one above par.
Overnight leader Nick Watney slipped back to five shots off the lead after following his day-one score of 67 with a 73.