Both teams brought lots to this game, CSN, Cork took the lead on 15 minutes from a free kick driven low to the bottom corner of goal.
The equaliser for Letterkenny IT came in the 32nd minute from Darragh McDaid.
The final score of the game came in the 85th minute from centre back Dylan Walsh, despite some good goalkeeping from keeper Gallen.
Colaiste Stiofan Naofa face NUIG in the league final on 18 February.
The LYIT still have the 2nd round of the CFAI Cup to look forward to, as soon as the Dundalk IT v National College of Ireland game is played.