Carnew, making their debut in the competition, more than held their own for most of this game but their inexperience cost them dearly.
The more accomplished St Mel's had a try in the opening half from Ciaran Connolly and a second by Mark Farrell, converted by Brian Kennedy to lead 8-0 at half-time.
On the changeover Carnew's Pat Nolan scored a penalty but that was to be their only score and the Longford side went on to add a try from John Kelly and a penalty by Ciaran Connolly to run out convincing winners.
ST MEL'S: D Honan; P Doherty, F Kirwan, J Byrne, J Duffy; D Sweeney, M Johnson; C Connolly, M Farrell, J Kelly, B Kennedy, P Gaffney, R McDermott, J Purdy, W O'Halloran. Replacements: G McGoldrick for Purdy; H Clifford for McDermott.
CARNEW CS: J Dempsey; E Kenny, D Burnell, E Murphy, P Culken; W Dillon, G Kelly; J Byrne, M Young, B O'Sullivan, D Kavanagh, S Hennessy, C Maher, D Cullen, P Nolan. Replace- ments: S Doyle for Kenny; S McDowell for Murphy.
Referee: T P Keenan.