Title holders Australia, who will cement their place in the semi-finals with a win, made one team change from their seven-wicket victory over England on Sunday.
Left-arm seamer Nathan Bracken is being rested to allow right-arm seamer Stuart Clark play his first match in the ensuing World Cup.
The Irish, as good as eliminated, also made one change, drafting in seam bowler John Mooney for batsman Peter Gillespie.
The weather was hot and sunny in Barbados, which is hosting its second game in the seven-week tournament. The final will be held at the Kensington Oval on April 28.
Australia: Ricky Ponting (captain), Adam Gilchrist (wicketkeeper), Matthew Hayden, Michael Clarke, Andrew Symonds, Mike Hussey, Brad Hodge, Brad Hogg, Stuart Clark, Shaun Tait, Glenn McGrath.
Ireland: Trent Johnston (captain), William Porterfield, Jeremy Bray, Eoin Morgan, Niall O'Brien (wicketkeeper), Kevin O'Brien, Andrew White, Kyle McCallan, John Mooney, Dave Langford-Smith, Boyd Rankin.
Umpires: Billy Bowden (NZ), Rudi Koertzen (RSA) and Third Umpire: Steve Bucknor (WI)
Match Referee: Ranjan Madugalle (SL).