The three-in-a-row dream lives on for Rockwell following their comfortable win in Tipperary.
This encounter was over as a contest by half-time as Rockwell had scored 18 points without reply.
It was a first half to be remembered for Rockwell centre Rory Parata, who scored all the points.
With Rockwell captain Aidan Butler in the sin-bin after 32 minutes, Castletroy improved and were rewarded with a try by Liam Cronin, converted by Conor Linehan, who had no joy with three first-half penalties that would have kept his side in touch.
However, Rockwell full-back Steve McMahon had the final say late on as he burst through the middle to touch down, with Parata converting.
Rockwell College – S McMahon; D O'Mahony, S O'Donoughue, R Parata, W Coffey; A Moynihan, B Riley; D O'Connell, S McNulty, J Maxwell; A Horgan, S O'Connor; J Feehan, S Dwyer, A Butler. Reps: J Bolger, D O'Dwyer, L Hickey, S O'Connell, J Brophy, R Horgan, E Mulcahy, A McMahon.
Castletroy College – P Butler; C Malone, M McCarthy, K Carroll, R Joyce; C Linehan, R Cunningham; C Bartley, L Cronin, A Clancy; R Larby, J O'Neill; B Burns, D Kennedy, R Murphy. Reps: E Fitzgerald, J Doyle, N Clohessy, C Humphreys, S Hoare, S Carey, J Fox, J Murphy.
Ref – D McCormack.