Harris' 62 was three strokes better than his previous best round on the Champions Tour and matched the 18-hole tournament record established by Gil Morgan in the second round in 2004.
Morgan is two strokes back and alone in second place after an opening-round, 7-under 64 at Oak Hills Country Club. Defending champion Mark McNulty shares third place one stroke further back with Jerry Pate, Dan Pohl and Lonnie Nielsen.
There were plenty of good scores on Friday -- 11 players are within five strokes of the lead -- but Harris stole the show.
Playing in the final group to tee off at the first hole, Harris opened his round with a bogey at the par-4 first when he three-putted from 20 feet. But after consecutive pars, the 53-year-old played his next seven holes at 7 under par.
Harris consistently made strong shots with his irons -- leaving himself with birdie putts no longer than 8 feet during the span -- and set up an eagle at the par-5 10th by knocking a 6-iron within 25 feet on his second shot.
His birdie-eagle run from No. 6 through No. 10 (he played the five holes at 5 under) is the best on the Champions Tour this year.
'I just kept going and tried to make every birdie I could,' said Harris, who has never won on the PGA Tour or the Champions Tour.
A poor drive at the par-4 12th led to his second bogey of the day, but Harris regained that stroke with a birdie at the next and went on to birdie three straight holes from the 15th to reach minus-9.
He rolled in a 20-foot putt for his final birdie of the day at the par-4 17th.
Harris needs a good finish here to make the top-30 and gain entrance to the season-ending Charles Schwab Cup Championship next week. He currently ranks 33rd on the money list with $471,350, but don't mention that to Harris.
'I can't worry about my position ... I've just got to go play,' Harris said after his stellar round. 'I didn't have a very good first half of the year ... but I know I have the game to play out here (on the Champions Tour).'
Morris Hatalsky and Mark James share seventh place at 5-under-par 66, one stroke ahead of four players tied for ninth.
Among the golfers tied for ninth place is Dana Quigley, who leads the Charles Schwab Cup Standings by 261 points over Hale Irwin. Irwin is tied for 19th place at minus-1.