Roscrea recovered from their devastating defeat by Clongowes in the Leinster Senior Cup final last Thursday to edge a nerve-shredding clash in Portarlington yesterday.
Kilkenny out-half Peter Lydon fired over a penalty before Roscrea captain Conor Finn did it all himself to bag a 50-metre try, converted by Bill Duggan.
However, two more strikes from Lydon made it 9-7 at the interval.
A Duggan penalty and hooker Denis O'Dwyer's finish from a pick-and-go put Roscrea 15-9 ahead with time slipping away.
Kilkenny were far from out of it, though, and replacement flanker Michael Triggs found a way over near the end, only for Lydon's conversion attempt to shave the wrong side of an upright.
Cistercian College Roscrea -- P O'Dwyer; C Brennan, S Layden, C Finn (Capt), M Mellotte (D Kirwan 38); B Duggan, G Gallagher; O Heffernan, D O'Dwyer, C Farrell (G Fallon 66), A McGrath, R Moloney, A Henderson, R Mooney, C Moloney (E Quirke 10).
Kilkenny College -- E Kelly; T Bulfin, F Horan, R Bailey-Kearney, S Sterling; P Lydon, D Leybourne; R Elmes (Capt), R Foot, G Condell (M Triggs 60), A Doyle, A Bernard-Day, S Delahunt, G Ridgeway, R Deacon.
Ref -- T Browne (IRFU).