Mason would spend most of his first two professional seasons in the AHL with the Binghamton Whalers, trapped behind the experienced Washington duo of Pat Riggin and Al Jensen who had combined to win the 1984 Jennings Trophy.

For the 1986-87 season, Mason was finally given a chance to stick in the NHL and responded in fine fashion, making 45 appearances and finishing amongst the top starters in the league in goals-against average and save percentage.

Mason made 54 saves total including 36 straight from the start of overtime in an epic goaltending duel with Kelly Hrudey before ultimately conceding the winning goal on a screened slapshot by Pat Lafontaine, eliminating the Capitals.

Mason would experience another highlight in the summer of 1987 when he was selected to the American team for the 1987 Canada Cup, although he didn't see any action as the 3rd goaltender on the roster behind superstars John Vanbiesbrouck and Tom Barrasso.

He was re-acquired by Washington for the 1989-90 to serve as backup to Don Beaupre but was unable to recapture the form he showed in his first stint and released at the end of the year.