Richie Baker's 12th minute strike separated the two sides in this challenge match at Tolka Park last night.
Although none of the treble-winning team were present the trophies were paraded before a crowd of 7,000 before the game.
The United team, which boasted former Irish youth centre half John O'Shea, included a mixture of youth and reserve team players with midfielder Jon Greening particularly impressive.
But it was Baker who stole the limelight with an instinctive goal after being played through by Carl Van Der Velden.
SHELBOURNE: Williams; Heary, McCarthy, Scully, D Geoghegan, D Baker, Van Der Velden, Fenlon, R Baker, S Geoghegan, G Haylock. Subs: Doolin for Fenlon half-time; Gifford for Heary 54 mins; Kelly for Haylock 61; O'Brien for Van Der Velden 69; O'Leary for Williams 84.
MANCHESTER UNITED SELECTION: Culkin; Hilton, Curtis, O'Shea, Clegg, M Clegg, Twiss, Wilson, Greening, Ford, Healy, Notman. Subs: McDermott for Hilton 56 mins; Steward for Twiss 71; Wellens for Ford 79.
Referee: J McDermott (Dublin).