He missed a birdie putt on the 18th hole, blowing an opportunity to equal the course record 61 that two-time defending champion R.W. Eaks shot in the first round last year at the Rock Barn Golf Club.
Gil Morgan stayed within two strokes of Haas before a bogey at the 18th left him 7-under 65, alone in second place.
"I got off to a good start (and) all of a sudden I was four-under and everything rolled from there," Haas, the 2005 winner, said after his best round on the Champions Tour this season.
Nick Price, Jerry Pate and Tom Jenkins all shot 6-under 66 and are tied for third.