Dave Mulcahy scored a consolation for the League of Ireland XI late in the game.
The League of Ireland XI were committed but short of quality, and it did not take long for United to break the deadlock.
Thirteen minutes in Gavin Peers looked to have dealt comfortably with Park's cross, but he lingered on the ball for an eternity and the South Korean blocked his clearance into the net.
Owen, returning from injury, added a second 10 minutes later. Park played him through, but the goal was about Owen's individual brilliance flicking a lob from a narrow angle over Gary Rogers.
Rooney was lively throughout the half, but missed a couple of chances to add to United's lead.
And there was concern for the Red Devils towards the end of the first half when Carrick hobbled off and down the tunnel.
Rooney and Owen made way at half-time for Hernandez and Dimitar Berbatov, and the Mexican impressed immediately with a poacher's finish on 47 minutes from Valencia's low cross.
As the second half continued the League of Ireland XI's defence was breached time and again. Valencia bustled through to score the fourth on the hour with a driven shot on his left foot then three minutes later Park added his second with a composed finish from Evans's pass.
Evans made it six by nodding in Valencia's cross before Mulcahy rescued some pride with a classy first-time finish from Conor Powell's pass.
Normal service was resumed moments later, however, when Ken Oman brought down Hernandez crassly in the area and Nani tucked away the penalty.