A much-improved second-half performance, sparked by replacement Sean Doyle, saw CBC Monkstown deservedly qualify for the last eight at a chilly but dry Donnybrook yesterday.
The opening half was eminently forgetable, high on endeavour but even higher on nervousness and basic mistakes; three missed penalties was about the extent of the action.
A big, strong CUS side had looked the more likely to break the deadlock, with centre James O'Kane and big-kicking full-back Adam Craig the most threatening.
Two minutes into the second half, Monkstown took the lead courtesy of a Ben Mahon penalty.
The CUS response was rapid, with O'Kane bisecting the posts following a late tackle on out-half James Cox.
While the penalty was perhaps justified, the yellow card issued to the game's outstanding individual Eoghan Clarke was questionable. As often happens in these circumstances, it was the side reduced to 14 that took the initiative.
Doyle's arrival coincided with an increase in CBC energy levels and when influential scrum-half Rob Jordan backed himself with a quick tapped penalty in front of the posts, from the ensuing ruck, Doyle accelerated through a half-gap for a brilliantly crafted individual try.
The ball then fell over agonisingly as Mahon was attempting the easy conversion.
O'Kane (55mins) and Mahon on the hour swapped well-taken penalties before the impressive Doyle delivered a clever disguised pass inviting Mahon through the gap and in under the CUS posts for the same player to add the extras and with it ensure a near unassailable 18-6 lead.
To their immense credit the Leeson Street school bounced straight back, with replacement Brendan Meehan the last to emerge from a near unstoppable driving maul.
Alas, it was much too little far too late as victory and with it a place in the quarter-finals went where it was most deserved.
CBC Monkstown: S Sweeney; D Porter, K Shaw, P Rogers (S Doyle 50), T O'Callaghan; B Mahon, R Jordan; M McGrath (C Byrden 51), A Holmes, E Clarke; J McAteer, H O'Neill (capt); R Courtney, M Hallam, J Halwax.
CUS: A Craig; O McGovern, S Quinlan (C Byrne 61), J O'Kane. L McConkey; J Cox, H Cronin; H Bodkin (S Butler 49), D Byrne, D O'Neill; D McCarthy (C O'Cleirigh), J O’Connor (S Russell 43); A Fleming (B Meehan 68), L Garvey, H O'Connor (capt).
Referee: B MacNiece (ARLB).