The pair played No. 18 four times en route to deciding a winner. After matching pars the first three times, Purtzer ran home an 18-foot birdie effort before Roberts stepped up to his 12-foot birdie try.
Roberts was unable to convert giving Purtzer his fourth Champions Tour title and second at this event. Roberts, who is winless in five starts this year, will go for his first win since the Senior Players Championship last October.
Tom Kite has also won this event twice since 2002.
Reigning Player of the Year Jay Haas joins those three players at Valencia this week. Haas, who is winless this year, hasn't finished outside the top six in his three starts this year, including a playoff loss last week to Bernhard Langer.
The GOLF CHANNEL will broadcast action of all three rounds starting at 6:30 p.m. (ET) each day.
The Champions Tour is off next week, but returns the following week with the Ginn Championship, where Keith Fergus won last year.