Chapman and Blake were 17 under. The teams of Bernhard Langer-Tom Lehman, Brad Faxon-Jeff Sluman, Scott Hoch-Jim Gallagher Jr., Craig Stadler-Kirk Triplett and Brad Faxon-Jeff Sluman were tied for second.
"The way it's all bunched up, it's all set up for somebody to shoot really low," Lehman said. "Like a 60. Or a 59."
The winning teams have shot a 10-under 62 or better in the final round each of the last four years.
Chapman and Blake bring a nothing-to-lose attitude into the finale. The two credited another of their Saturday playing partners, Peter Jacobsen, for their second-round run. Jacobsen, teaming with D.A. Weibring, birdied six of his first eight holes and created "momentum" for all four players in the group.
Chapman parlayed the positive vibes into six straight birdies to start the second nine. Blake added a birdie at No. 8, a par 3 and their 17th hole of the day, courtesy of a 40-foot bunker shot.
"We made the turn, and I just kind of wanted to get in the golf cart and watch Roger," Blake said.
Chapman's been worth watching for almost a year now. He won his senior tour debut last May in the Senior PGA Championship and won again two months later at the U.S. Senior Open.
"He may not have won a whole lot, but he's been a good player for a long time. He's never been a slouch," said Lehman, who along with Langer will play with Chapman and Blake in the final group. "He just maybe lacked that little something extra to get over the top. And I think he's found it."
Sam Snead and Gardner Dickinson won the inaugural event in 1978 at Onion Creek in Austin, Texas, sparking interest that led to the creation of the senior tour.