Peter Jacobsen, one week removed from laser back surgery, also posted a 64 in round two and is alone in second place at minus-12. R.W. Eaks, one of six co- leaders after the first round, carded a 5-under 66 on Saturday and has third to himself at 11-under-par 131.
Ben Crenshaw, also a co-leader from Friday, shot a 4-under 67 as he looks for his first Champions Tour win. He is tied for fourth place with Joe Ozaki, who posted a 64, at minus-10.
Haas was also atop the leaderboard after the first round and wasted little time in distancing himself from the pack. From the right rough, Haas hit a beautiful approach to three feet to set up birdie at the second. He birdied the par-5 third, then drained a six-footer at four to polish off three consecutive birdies.
The reigning Champions Tour Player of the Year birdied the seventh to reach 10 under par for the championship. He closed his front nine with another strong iron shot from the rough, this time a 9-iron at the ninth that stopped three feet from the flagstick. Haas kicked in the birdie putt and moved into the lead.
Haas struggled to get anything going on at the start of his second nine. He parred his first five holes on the back side at Newport Beach and some times missed some makable birdie tries.
He was now tied for the lead with Jacobsen and Eaks at 11 under par when he missed the green with his second at the par-5 16th. Haas nearly found the surface, but instead played his third to 10 feet. He drained the birdie putt to move into sole possession of first at minus-12.
Haas hit an errant drive at 16, but saved par. He used a 7-iron at the par-3 17th and stuck his ball three feet from the hole. Haas converted the birdie putt to extend his margin to two.
At the par-5 closing hole, Haas could not reach the green with his second shot. He played a nice shot to eight feet, but could not make the birdie effort.
Despite the missed opportunity at the last, Haas is still in control as he seeks his first win of the season on the elder circuit. He has two runner-ups and is second in both earnings and Charles Schwab Cup points, but would like to return to the winner's circle.
'The shots are there if you can pull them off,' said Haas. 'I had a hot putter today. Who knows what it's going to take to win here? There are a lot of good scores being shot.'
Jacobsen was equally strong on Saturday. He birdied one and three, then bogeyed the eighth, but that would be the last mistake of the round for Jacobsen.
He birdied the ninth, chipped in for birdie at the 10th, then birdied No. 11 to get to 9 under par. Jacobsen chipped in again for birdie, this time from short of the green at 14, and tapped in a short birdie putt to get to minus-11 at the 15th.
At the closing hole, Jacobsen left himself a four-footer for birdie. He drained that putt to get within one of Haas' lead as he looks for his third Champions Tour win and first non-major.
'From the operating room, to the interview room,' joked Jacobsen, whose only two wins on the tour are the 2004 U.S. Senior Open and 2005 Senior Players Championship. 'The guy we're all chasing is so good with his short clubs and putter that I'm going to have to continue to chip and putt like I did to have any chance.'
Tom Purtzer, the fourth overnight co-leader, shot a 3-under 68 and is tied for sixth place with Craig Stadler (64), Rich Karbowski (66) and Bruce Lietzke (66) at minus-nine.
Eduardo Romero and Fuzzy Zoeller, the final co-leaders from Friday, both shot rounds of 2-under 69 and share 10th place with Mark O'Meara, who posted a 5-under 66 on Saturday. The trio is knotted at 8-under-par 134.