As the scores were level at 2-2 upon the full-time whistle, a penalty shootout was required to separate the sides and Mark McNulty proved to be the hero as he saved twice to allow Dion Dublin to slot home United's winner.
It was fitting that the first ever soccer goal scored at this famous G.A.A stadium was scored by a Cork man as Denis Irwin rifled his penalty into the bottom right corner after Wes Brown was fouled inside the area by Johan Mjallby.
The Celtic and Republic of Ireland legends ought to have levelled the scores in the 21st minute but Kevin Kilbane somehow sliced wide of an open goal from a few yards.
United doubled their lead midway through the first half when Louis Saha raced onto a Ryan Giggs through ball before coolly rolling the ball past the keeper and into the far bottom left corner of the net.
Robbie Keane became the first Dubliner to score a soccer goal at this venue as he halved the deficit just before the break, cutting in from the end line before drilling his shot in from close range.
Having worn Celtic jerseys in the first half, Martin O’Neill’s side changed into Republic of Ireland jersey’s for the second and they levelled the scores with another memorable strike with nine minutes remaining.
Robbie Keane’s clever lay-off found Colin Healy inside the area and he fired the ball past his former Cork City team-mate Mark McNulty, both of whom were close friends of Liam Miller.
But in the end, it was Manchester United who emerged victorious as McNulty saved from Robbie Keane and Ian Harte to allow Dion Dublin to score the decisive spot kick.
Republic of Ireland/Celtic XI: David Forde; Stephen Carr (Stephen Kelly 45), Richard Dunne (Kenny Cunningham 45), Johan Mjallby (Colin Healy 45), Ian Harte (Stephen McManus 45); Damien Duff (Tosh McKinlay 45), Paul Lambert (Graham Kavanagh 45), Stillyan Petrov (Andy Reid 45), Kevin Kilbane (Stephen McPhail 45); Shaun Maloney (Kevin Doyle 45), Robbie Keane.
Manchester United: Kevin Pilkington (Mark McNulty 60); Gary Neville (Michael Clegg 45), Wes Brown, Mikael Silvestre, Denis Irwin (David May 45); John O’Shea, Paul Scholes (Louis Saha 70), Nicky Butt (Roy Keane 60), Ryan Giggs (Quinton Fortune 60); Louis Saha (Dion Dublin 45), Alan Smith.
Referee: Graham Kelly (Cork).