Phil Mickelson in a league of his own at Pebble Beach Pro-Am

Phil Mickelson closed in on his fifth victory in the tournament as he shot a six-under 66 to take a two-shot lead in the AT&T Pebble Beach Pro-Am.

It is the first time the left-hander has held a 54-hole lead on the PGA tour since the 2012 US Open at Merion.

"It's been awhile since I've been in contention and it would mean a lot to me to be able to play a good final round tomorrow," Mickelson told reporters.

"And as well as I've been hitting the ball, the score was great, but the ball-striking wasn't indicative of how I've been hitting it. So I would like to get that dialed in for tomorrow's round.

"It's fun to be back in the thick of it."

Mickelson required only 21 putts to leave him 16-under, two ahead of Japan's Hiroshi Iwata, who shot a 69 at Spyglass Hill.

Freddie Jacobson sits in third, three shots behind Mickelson after a 68 at Monterey Peninsula, alongside Sung Kang, who had a 70 at Pebble Beach.

Jason Day shot a 68 at Pebble Beach to lie six shots back, while Justin Rose held a share of the lead at one point at 13 under but four bogeys and no birdies over the final 11 holes saw him sign for a 72, seven shots behind.