Hubert Green, who ousted Hale Irwin on the seventh extra hole to win the Long Island Classic last Sunday, was three strokes off the lead after a round of 5-under-par 67.
Mason, who earned his first career victory on the Senior Tour as a Monday qualifier at the NFL Golf Classic in June, picked up four birdies and one bogey on the outward nine at the TPC of Twin Cities. He made the turn at 3-under before torching the back half to take the outright lead.
'After the first couple of holes I was okay,' said Mason, who established a new course record. 'Today there was a fantastic gallery out there. This round reminds me of my first round at the NFL Golf Classic.'
At the par-4 10th, Mason hit his second shot to 15 feet for birdie. He hit a 5-iron to 12 feet for birdie at the 13th and nearly added another birdie at the 14th after he failed to convert from four feet.
Mason picked up where he left off on the following hole. He drained a 12-footer for birdie and knocked his approach to eight feet for birdie at the 16th. Mason made it three in a row with a 20-foot birdie putt at the 17th for his best career round on the Senior Tour.
'It was certainly a great thrill to play with two legends,' said Mason, who was paired with Arnold Palmer and Miller Barber Friday. 'I knew I'd play with Arnold Wednesday morning. He's always been a hero of mine.
'Hopefully, I won't be as nervous tomorrow as I was in the second round at the NFL Golf Classic,' said Mason, who carded a 73 in the second round en route to his first career win at Upper Montclair Country Club.
Irwin played a bogey-free round to finish alone in second. The all-time winner on the Senior Tour collected three birdies on the front side and added another three on the inward nine for a round of 66.
'Good start,' said Irwin, who has two playoff losses in his last three starts. 'Last week was last week. I tried to take some positives from last week.'
Leonard Thompson, who won this event in a playoff over Isao Aoki in 1998, finished as part of a large group at 4-under-par 68. Thompson was joined by Fuzzy Zoeller, Sammy Rachels, Allen Doyle and Rocky Thompson in a tie for fourth.
Defending champion Bruce Lietzke was one shot further back at 3-under-par 69 alongside Wayne Levi, Jerry McGee, Larry Nelson and Hugh Baiocchi.
Full-field scores from the 3M Championship