The 1998 champion here, Mickelson had what was expected to be the daunting task of playing the Spyglass Hill course, the toughest of the three courses being used here. But he had little trouble en route to a record day.
Mickelson picked up where he left off last week, when he won the FBR Open by five strokes - his first victory since the 2004 Masters.
He recorded birdies on seven of his first 11 holes. On the back nine, Mickelson birdied the 14th and added another two to close his round to establish the course record. Dan Forsman (1993) and Steve Lowery (1995) shared the previous course record of 64.
"I don't feel surprised right now," Mickelson said. "Normally when I have a very low round like that I think, `Oh, wow, that's great.' But it feels like the way I'm hitting it I should shoot that."
Mickelson has a three-shot lead over Charles Howell III, Kevin Sutherland, Hunter Mahan, Davis Love III and Daniel Chopra.
The tournament is being played on three courses, Spyglass Hill, Pebble Beach Golf Links and Poppy Hills, with Pebble Beach hosting the final round.
Already with a win under his belt this year, the world No 1 Vijay Singh is making the first in a long line of title defences. He also played the Spyglass course and shot a disappointing 73.
Scores, Digest, page 64