Tameifuna weighed in at a colossal 142 kilos, 24kg heavier than Mason, who did have height and reach advantages.
It looked as though the Chiefs prop had knocked Mason to the floor in the first round, but the referee did not rule a knockdown.
Mason won the bout on points, though he felt he did not deserve it.
“I don’t think I won that fight,” said Mason.
“I was easily going to give it to Ben. Sorry Ben.”
It was Tameifuna’s second defeat to a rugby league player, having lost to Sam Thaiday last year in a similar charity bout.
League also emerged victorious from another fight on the bill, with former NZ Warriors hard man Monty Betham battering former All Blacks flyhalf Carlos Spencer, and winning on a Technical Knock-oout.