A club pro from Dillard, Ga., Mason proved he is no flash in the pan, setting a course record, matching a tournament mark and recording his lowest round on the Senior PGA Tour with an 8-under-par 64.
Baseball Hall of Famer Johnny Bench shot an 81.
"Certainly a great thrill to play with two legends," Mason said. "I knew I'd play with Arnold on Wednesday morning. He's always been a hero of mine."
Mason, who in June won the NFL Golf Classic as a Monday qualifier, opened the round by chipping in from 40 feet for birdie. After a bogey at the second hole, he two-putted for birdie at the par-5 third.
Mason parred three straight holes before playing the final 12 in 7-under. Along the way, he had five birdie putts of at least 12 feet.
"I feel good with the round," he said. "I putted well and hit it off the tee well after the first couple of holes."
Despite missing a four-foot birdie putt at the 18th hole, Mason set a course record, breaking the old mark by two stroke. He became the sixth player in tournament history to shoot a 64.
Mason also recorded his lowest round as a Senior Tour member. He shot an opening-round 65 en route to his first career title in June.
"This round reminds me of my first round at the NFL Golf Classic," Mason said. "Hopefully, I won't be as nervous tomorrow as I was in the second round then."
On Saturday, Mason will play with Irwin, who has two titles this season but none since March. In 18 starts this season, he has 15 top-10s, losing a pair of playoffs in the past month.
"Last week was last week," said Irwin, who is 0-5 in playoffs on the Senior Tour. "That's gone now."