Joe Inman carded a 7-under-par 64 to take second place. Morris Hatalsky is one stroke further back at minus-6, while John Bland, David Eger, Fuzzy Zoeller and Keith Fergus share fourth place at 5-under-par 66.
Purtzer got hot early and it carried him throughout his round. He drained a birdie putt at the first at Newport Beach Country Club, and came back with another birdie at the third.
The 2003 SBC Classic winner rolled in another birdie at the fourth and made it three straight when he birdied the fifth. Purtzer then sank a seven-foot birdie try at the 10th to get to 5 under.
'I hit some good shots on the front side,' said Purtzer. 'Usually when you go low, you tighten up. I did start to get anxious on the back side.'
The 52-year-old sank another birdie try at the 12th. After converting a birdie at the 14th, Purtzer jumped to minus-9 when he sank a five-footer for eagle at the par-5 15th.
Purtzer came right back to birdie the 16th. He had a chance to shoot 59 with the 18th being a par-5, but he missed the green. He did manage to get up-and-down for birdie to shoot 60. It was the fifth time in Champions Tour history that a player has shot 60.
'I really wasn't expecting much,' a subdued Purtzer said. 'I've been having trouble driving the ball and you've got to hit the fairway here. Once I made the eagle, I thought I had a chance at 59.'
Inman nearly matched Purtzer's magic, but a pair of front nine bogeys side- tracked him. He picked up birdies at the second and the par-4 fifth, however, Inman dropped a shot at No. 6.
The 56-year-old came right back to birdie the par-4 seventh. Inman again faltered to a bogey at the eighth to drop back to minus-1 but fought right back to birdie the ninth.
Inman dropped in back-to-back birdies from the 11th and again from the 14th to move to six-under. The two-time Pacific Bell Senior Classic winner birdied the 17th for solo second place.
'I was just magic today with my putter,' said Inman. 'I only made two bad swings all day. I've improved each week this year. I'm looking forward to playing now. This is the best place to be when you're playing well.'
John Jacobs, the reigning Senior PGA champion, posted a 4-under-par 67. He is joined there by Lonnie Nielson, Leonard Thompson and Bob Eastwood.
Champions Tour rookie Mark McNulty is one stroke further back at minus-3. He stands alongside Dave Stockton, Bruce Summerhays, Bobby Wadkins, Tom Wargo, Isao Aoki, Andy Bean and Bruce Fleisher in a tie for 12th.
Rodger Davis, the defending champion, opened with an even-par 71.