He stood at 21-under, 198 with one round left, while Fred Funk was next at 203 after a 68. Billy Mayfair, who carded a 69, was another stroke behind after Saturday's play.
Tiger Woods excited his gallery with six birdies for a flawless 67, but it was only enough to move him into a tie for fourth with Jim Furyk and Vijay Singh, seven strokes off the lead.
Duval's round included six birdies and one bogey, his only blemish coming at the par-four 16th where he drove into a fairway bunker, ending a run of 44 holes without a bogey.
"Anytime you make five or six birdies in a round you can't complain," said Duval, who had 10 birdies in his course-record tying second round.Reuse content