The Waterford school were twice forced to come from behind against an inspired 10-man St Benildus, with Conor Coad, the grand-nephew of former Shamrock Rovers legend Paddy Coad, twice scoring to drag the Waterford side level.
Despite losing Karl McGrath on five minutes to a red card for a professional foul, St Benildus showed immense courage and managed to take the initiative, going ahead through a Conor Buter long-range shot three minutes before half-time.
Concerted second-half pressure from De La Salle eventually yielded an equaliser on 70 minutes, when the impressive Coad latched on to a Chris Kervick cross to beat Keith Finn with a sweet volley.
However, St Benildus regained the lead two minutes into extra-time when Paul Connolly kept his cool to find the net from 20 yards, only for Coad to grab his second three minutes after the turnaround following a neat cut-back by Kevin Flynn.
The gripping penalty shoot-out went all the way to sudden death and, after Whitty had saved David Byrne’s attempt, he stepped up to drill home the decisive kick.
ST BENILDUS COLLEGE: Keith Finn; Michael Rogers, Stephen McAuliffe, Tadgh Healy, Karl McGrath, Ben Meegan, Alex Oates, Conor Buter, Paul Connolly, Daniel Byrne, Paul Mannion.
Subs: Conor Day, Brian Reilly, Ceelan Simon, David Byrne, Mark Brennan.
DE LA SALLE, WATERFORD: Sean Whitty; Mark McManus, Gavin O’Donevan, Adam Potter, Patrick Fitzgerald, Conor Whittle, Colm Morris, Adam Galibert, Chris Kervick, Kevin Flynn, Conor Coad.
Subs: Adam Deegan, David O’Leary, Eoin Kindlon, Conor Kirby, Luke Brown.
Referee: Lee Bevans (Wicklow).