Purtzer was joined in the lead at 7-under-par 135 by Graham Marsh (69) and first-round leader Bob Eastwood (70). The threesome has eight players within two strokes of their lead.
Vicente Fernandez and Joe Inman each posted 68 to get to minus-6. They share fourth with Dave Eichelberger (69).
Allen Doyle, Jay Haas, Walter Hall, John Harris and defending champion Mark Johnson are one stroke further back at 5-under-par 137.
Each of the three leaders had very different rounds. Purtzer birdied two of his first three holes to move to 5 under. He picked up another birdie at the sixth.
Purtzer, who has won once in each of the last three seasons, tripped to back-to-back bogeys from the seventh. He recovered those strokes when he holed his 7-iron approach shot for eagle on the par-4 10th at Newport Beach Country Club.
The 55-year-old traded a birdie for a bogey from the 12th and again from 15. Purtzer rolled home a birdie putt on the par-5 closing hole to end at minus-7.
'I really haven't hit it too good lately, but today I had more chances to make birdies and I drove it better,' Purtzer said. 'It was a much better round than I have had the past few weeks. I'm encouraged.'
Marsh struggled to bogeys on Nos. 1 and 4 to fall to minus-3. He parred his next six holes before getting one stroke back with a birdie at the par-4 11th.
The Australian ran off three straight birdies from the 15th to join Purtzer at 7 under.
Eastwood, who played alongside Marsh, opened with six consecutive pars. He moved to 7 under with a birdie on the par-4 seventh. However, Eastwood bogeyed four of five holes from the ninth to tumble back to minus-3.
The 60-year-old fought back with birdies on the 14th and 15th. Eastwood parred 16, but dropped in back-to-back birdies from the 17th to grab a share of the lead.
Mike McCullough and Jose Maria Canizares each carded rounds of 4-under 67 to move to 4-under-par 138. They share 12th place with Bruce Lietzke (72), Brad Bryant (70) and David Eger (70).