'It's been a lot of fun so far. I love these golf courses, I love playing them the way I've played them,' said Mickelson. 'I certainly love being in the position I'm in.'
Greg Owen, who tied for fourth at the 2004 Q-School, eagled the par-5 18th at Poppy Hills to take second place at 13-under-par 203. Jose Maria Olazabal, Tim Clark, Kevin Sutherland, Andrew Magee and Paul Goydos tied for third at 11-under-par 205.
Mickelson tackled Pebble Beach Golf Links on Saturday, one of three courses in rotation over the first three rounds along with Spyglass Hill and Poppy Hills, and will get another shot at Pebble in the final round where he will look to win in back-to-back weeks on the PGA Tour for the first time in his career.
'I want to go out tomorrow and play a good solid round,' said Mickelson, who won the FBR Open last week. 'I've been playing well, I don't want to look at it any different.'
Mickelson was on a record-setting pace since he set the new course mark at Spyglass Hill with a 62 in the opening round. He established a new 36-hole tournament record on Friday and got right back to business in round three with a birdie at the par-4 fourth.
He drained an 18-footer for a birdie at the par-3 seventh and knocked his second shot within 12 feet of the hole at the par-4 eighth. Mickelson converted the birdie try to reach 18 under around the turn, but gave that shot back with a bogey at the par-4 10th after a poor bunker shot.
Mickelson was unflappable, however, and dropped his approach inside 6 feet for a birdie at the par-4 13th. He then played his second shot to 14 feet at the par-4 16th and sank the uphill birdie putt to move to minus-19.
At the par-5 18th, Mickelson ran his second shot down the fairway and lofted his third within 5 feet of the cup. The reigning Masters champion ran home the short birdie putt to secure a comfortable advantage with one round to play.
'I know the guys right behind me are coming after me,' he said. 'Right now I don't want to leave myself open. I want to win this thing tomorrow.'
Owen had an uneventful front nine with eight consecutive pars until his first birdie of the day at the par-5 ninth. The Englishman continued to play steady golf on the inward half with a birdie at the par-5 12th and another at the par-3 15th to join a group at 11 under.
The 32-year-old then hit a 4-iron within 12 feet of the hole at the 18th for the closing eagle to move into second place alone.
'You just have to go out and try to make birdie every hole,' said Owen. 'Phil is obviously going to need to slip up a little bit for me to catch him, but it's golf, anything can happen.'
Mike Weir, Darren Clarke, Jeff Sluman and Arron Oberholser share eighth place at 10-under-par 206.
Billy Andrade followed at 9-under-par 207 after a remarkable round of 63 at Pebble Beach. He was joined by Robert Gamez, Graeme McDowell and Richard S. Johnson in a tie for 12th.
The 36-hole cut fell at 4-under-par 212 with 64 players qualifying for the final round.
World No. 1 Vijay Singh capped off a disappointing week with a 73 on Saturday to finish at 3-over-par 219 for his first missed cut since last year's Buick Invitational.