Chapman's performance put him at 14-under 199 following 54 holes at Harbor Shores in Michigan -- matching Sam Snead's three-round tournament record set in 1973.
John Cook was alone in second place at 5-under. Cook fell to a 2-under 69 Saturday after having shared the second-round lead.
Hale Irwin, seeking his fifth Senior PGA championship, also registered a 69 while Steve Pate knotted him for third at 7-under 206 with a 4-under 67 Saturday.
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