Purtzer's 4-under 68 left him at 10-under-par 134 after 36 holes. He is seeking his fifth Champions Tour victory and second this season after winning the AT&T Champions Classic.
First-round leader Tom Watson posted an even-par 72 Saturday and is tied for second place with Kirk Hanefeld (66), Jack Ferenz (66), R.W. Eaks (64), Tom Jenkins (69), Keith Fergus (69) and reigning Player of the Year Jay Haas (66) at 137.
"I made dumb bogeys today that really cost me," Purtzer said. "But I hung in there and brought it back a little bit. Fortunately I made enough today that I feel good for tomorrow. We're going to have to make a lot of birdies tomorrow."