A powerful finish underlined Rockwell's dominance as they booked their semi-final spot when they overcoming Crescent.
The first half's early exchanges were more closely contested with Rockwell going into an early lead following an Alan Flannery try which John O'Sullivan converted.
Crescent hit back with a try from David Murphy but that was as good as it got for them.
Ten minutes into the second half, Crescent had a player sent to the bin and Rockwell took advantage with superb try from Sam Tarleton which O'Sullivan converted.
By this stage the Rockwell pack was on top and another try arrived courtesy of Josh O'Dwyer, who raced clear from 35 metres, with O'Sullivan converting again.
To put the icing on the cake O'Sullivan registered a splendid try two minutes from the end and added the extras once more.
Rockwell College - J O'Dwyer; P Wall, S Tarleton, A Flannery, T Tobin; J O'Sullivan, A Maher; D Foley, D Fanning, M Burke; L Fogarty, B O'Dea; C Kelly, R Anglim, L Shine. Reps: C Meaney, C Ryan, J Browne, M Bergin, K Grogan, O Fagan, B McCarthy, M Mulligan, H Buttimer, D Achimugu.
Crescent Comprehensive - B Cosgrave; D O'Shea, D Casserley, D Rickard, T O'Sullivan; B Davey, J Duggan; E O'Sullivan, J Rickard, B O'Sullivan; D Doyle, S Malone; J McKeogh, P Dolphin, B Scott. Reps: C Henchy, L Moloney, E Quinn, R Quinn, D O'Grady, R Herbert, E Cantillon-Mann, G Kelly, D Murphy, C O'Halloran.
Ref - T O'Donoughue (MAR)