Kilkenny College will be grateful for the accurate kicking of out-half Russell Armstrong as they contemplate another cup outing following this successful opener.
Late second-half tries by winger Philip Furney and wing forward Geoffrey Kenny helped turn defeat into victory for Kilkenny.
However, Armstrong's four successful penalty kicks and a conversion were at least as important to Kilkenny's cause.
Apart from an equalising penalty by Mick Costigan in the 10th minute, the winners led for most of the first half and were 9-3 in front at half-time.
St Gerard's went ahead in the 48th minute when Steve O'Donovan scored an excellent try, Simon Hunt running half the length of the field after intercepting a Kilkenny pass.
They led again thanks to a second Costigan penalty in the 53rd minute, but could not recover following Kilkenny's brace of match-winning tries inside the last five minutes.
Kilkenny College: R Deacon; B Walsh, D Armstrong, S Dalton, P Furney; R Armstrong, R Jones; B Gill, C Gee, K Gill, J Kidd, W Cooper, G Kenny, K Williams, R Whitford. Replacement: W Gethings for Deacon.
St Gerard's: S O'Donovan; N Crean, B Behan, C Vance, D Devlin; S Hunt, J O'Toole; J Kinsella, A Durkan, B Howard, P Gordon, N O'Brien, R Moran, D Silverlock, M Costigan. Replacement: C Mandal for Howard.
Referee: C Brannigan.