Tiger Woods stormed into the lead at his own Northwestern Mutual World Challenge tournament as Graeme McDowell moved up to fourth.
Woods, who plays host at the Sherwood Country Club in California, took full advantage of the birdie opportunities that came his way to tie his own course record.
A 10-under-par second round of 62 put him two clear of overnight leader Zach Johnson and on 11-under-par overall.
Behind him there were encouraging signs from Northern Ireland's Graeme McDowell, but Rory McIlroy had a day to forget with a five-over 77.
Defending champion Graeme McDowell, who also triumphed in 2010, carded a five-birdie 67 to end the second round alone in fourth, six shots off the pace.
McIlroy’s 77 left him joint 16th in the 18-strong field.
The Northern Irishman struggled all day, with a double bogey at the fourth and further dropped shots at the eighth, 12th, 13th and 14th, but the low point came with a quadruple-bogey at the 16th.
Woods' day-two efforts were a far cry from his opening round, which began with a bogey on the first before he made gains at five and 11.
Twenty-four hours on Woods kicked off with a birdie at the first, repeating the trick on the second hole before further gains at five, seven and eight.
The birdies continued after the turn as he picked up shots at 10, 11, 13, 14 and 16, before a pair of pars finished off a blemish-free round.
Johnson looked in similarly sweet form as he birdied three of the first five holes, but he parred the next 12 there before picking up an extra stroke at the 18th to put him clear in second. Matt Kuchar was a shot behind on eight under.