Midfielder Sione Osamu then crossed, with Mason keeping a spotless kicking record, for 35-0 at halftime.
Osamu started the second half as he ended the first, scoring in the opening minute, before first-five Harry Godfrey added his name to the sheet after another period of sustained pressure.
St John's then got onto attack to score their first try at 45-7, but Collegiate quickly reasserted themselves as both Hadleigh O'Leary and Osamu raised their hat tricks, while after a couple of misses, Mason converted both those tries.
The home side then scored off an intercept in the last minute.
"Another good team effort with Hadleigh O'Leary and Osamu obviously prominent in attack, but lots of good work being done by their inside backs to create for them," said Simpson.
"In the forwards, captain Henry Kilmister is leading by example, with young Tom Pease continuing his fine form and locks Hunter Morrison and Joe Abernethy offering more each game."
Collegiate will now have a home game with Francis Douglas Memorial College, kickoff 12pm.