The odds-on favourites for the News & Star trophy played below their best and shot a staggering 18 wides over the hour.
There was plenty of spice in the first half as De La Salle chiselled out a narrow half-time advantage (0-10 to 1-6), Paul O’Brien scoring Tallow’s goal.
Two O’Brien frees nudged Tallow back in front early in the second period as they showed no sign of bowing to the three time champions. Jake Dillon then equalised before Keane struck the decisive blow on 38 minutes.
Shane McNulty passed to the full-forward 25m out to the right of the posts and he unleashed a dipping shot to the top corner that gave Shaun O’Sullivan no chance (1-11 to 1-8).
Thomas Ryan reignited the tie briefly on 53 minutes but De La Salle had enough in the tank to hold on.
Scorers for De La Salle: J Keane 1-2 (1f); J Dillon 0-4 (4f); D Twomey, P Nevin 0-3 each; J Mullane 0-2; D Greene, A Farrell 0-1 each.
Scorers for Tallow: P O’Brien 1-6 (5f); T Ryan 1-2; E Sheehan 0-1.
DE LA SALLE: J Coady; O Keevers, I Flynn, S Dalton; C Watt, K Moran, S McNulty; D Greene, D Twomey; P Nevin, J Dillon, J Kennedy; A Farrell, J Keane, J Mullane.
Subs: J Sage for Farrell (40); B Phelan for Watt (40); B Cunningham for Greene (55).
TALLOW: S O’Sullivan; M O’Brien, D O’Brien, K Kearney; J Murray, K Geary, R Beecher; J Henley, P O’Brien; A Kearney, Bob McCarthy, J Beecher; E Sheehan, M Curley, T Ryan.
Subs: Brian McCarthy for R Beecher (35); S Feeney for Henley (40); J Henley for J Beecher (53); S McCarthy for Curley (53); J Tobin for Bob McCarthy (58).
Referee: D O’Leary.