St Columba's ran in three second-half tries to see off the stiff challenge of St David's at Seapoint.
St David's took an early lead through Cian O'Sullivan, but Richard Barrow and Kevin Daly, along with seven points from Michael Quinn's boot, saw St Columba's take full control.
Daly went over for his second try before Alan Wildes got a late consolation score.
SCORERS: St Columba's: K Daly 2 tries, R Barrow try, M Quinn 2 cons and pen, M Garcia pen; St David's: A Wildes try and con, C O'Sullivan try.
ST COLUMBA'S: M Garcia; K Daly, R Van Rampelberg, J Horsey, A Musgrave; T Reade, H Spiller; R Barrow, B Sadek, P Temple, J Mannion, L Abudarham, C Lyons, H Gervais, T Nolan. Replacements: M Quinn for Garcia, A McArdle for Temple (both half-time).
ST DAVID'S: S O'Brien; N Smith, B Glendon, A McFadden, A Maher; C O'Sullivan, R Linton; A Wildes, D Tyrrell, A Kavanagh, F Bennett, S Hayes, J O'Connor, C Taylor, S Richardson. Replacements: K Higgs for Maher (half-time), C Connolly for Higgs (54 mins).
