He broke the tournament record of 63 set by Fred Couples in 2012 and matched by Gene Sauers in 2017.
The 56-year-old Estes had a 64. He's winless on the 50-and-over tour.
"It would mean a lot," Estes said. "I haven't won a tournament since 2002 at the Kemper on the PGA Tour. ... I've been through a lot. I've worked hard for the most part on my game, equipment, training, stuff like that. I'm just enjoying hitting more quality shots and putting better, too."
Retief Goosen (67) and Paul Broadhurst (67) were 8 under. Goosen won the Hoag Classic a month ago in Newport Beach, California, in the last Champions event.
Alex Cejka (66), Doug Barron (67) and Paul Goydos (68) were 7 under.
Padraig Harrington, set to play in the Masters next week, was 5 under after a 72. Bernhard Langer, also headed to the Masters, was even par after a 71.