Chapman finished a 10-under 270, two shots better than four competitors tied at minus-8 at Indianwood Golf & Country Club.
The Briton also took the Senior PGA title in May at The Golf Club at Harbor Shores in Michigan.
He is the fourth player in Champions Tour history to win both titles in the same year. The others include Gary Player, Jack Nicklaus and Hale Irwin.
NBC reportedly holds celebs hostage to Jimmy Fallon's show
Ray Liotta sues skin care company over use of likeness