It took a rocket of a drop goal from full-back Fionn Higgins in the last minute to seal victory for Roscrea against Gonzaga at Donnybrook.
This was one that could have gone either way as both teams enjoyed spells of dominance in an enthralling tussle.
Roscrea out-half Tim Foley nudged his side ahead with an 18th-minute penalty after a knock-on was touched by a player ahead of the handler.
Gonzaga's quick tempo was causing Roscrea problems, though, scrum-half Dermot Lavelle breaking out of defence on a 60-metre surge that eventually ended with Lavelle sniping over at the edge of a ruck to give them a 7-3 interval lead.
The topsy-turvy nature continued when turnover ball was flashed left for Roscrea centre Cormac Brennan to put Higgins in under a tangle of bodies at the left corner. Foley converted from under the stand.
Gonzaga came storming back and sustained pressure resulted in Roscrea openside Marc Kelly seeing yellow for an infringement close to his own line.
Then, hooker Paddy Finlay was held up over the whitewash. But, Gonzaga stayed patient. The ball was worked left for impressive full-back Andy Marks to slip two tackles for a try, converted by McKeon, in the 46th minute.
Foley's monster kick to touch enabled Roscrea to set up a line-out and maul that cracked the Gonzaga defence for lock Daniel Trayers to rumble over for a 15-14 lead in the 55th minute.
It was frantic stuff, with Gonzaga opting for the tap-and-go to discomfort the bigger Roscrea forwards and Foley aiming to pin the Dublin boys back in their '22.' Roscrea eventually made it into the danger zone and began to wind down the clock, even passing up a kickable three points until the ball was cleared for Higgins to drop a goal in the last minute.
Roscrea – F Higgins; T Carroll, C Brennan, D Corcoran, R Wharton; T Foley, R Lavery; J Walshe, P Ennis, O Heffernan, K Buckley, D Trayers, M Keane, M Kelly, R Moloney (capt)
Gonzaga – A Marks; H Gowing, H Caslin, K O'Connor, P Keenan; C McKeon (capt), D Lavelle; R Byrne, P Finlay, R Barry, E Byrne, C Kenny, J Carter, J Doyle, M McVey
Ref – A Fogarty (Leinster)