The nine-time world champions were in dominant form against the Irish as Australia ran in nine tries without reply in the final group match in Limerick.
Ireland struggled to make any impact on the Australia defence and were left frustrated by a lack of possession.
Five different players crossed the whitewash in the opening half as the Kangaroos showed a neat passing game interchanged with kicks when required.
Jarryd Hayne opened the scoring fin just the second minute after Brent Tate had drawn his marker to send the winger over in the corner.
Half-back Cooper Cronk added a second nine minutes later, but Ireland began to find their feet and were able to repel the waves of Australian attacks.
However, in the last 11 minutes of the half, Ireland's resistance was broken as Greg Bird, Brett Morris and Billy Slater all took advantage of the tiring defence to go over.
Cameron Smith successfully converted three of his five attempts to give Australia a 26-0 lead at the break.
The Kangaroos were made to wait 17 second-half minutes before they could add to their tally, but the points quickly began to flow once Australia got back into their stride.
Cronk grabbed his second try to get them going again, and when Daly Cherry-Evans went over after an hour and Corey Parker converted Australia had notched their 100th point of the tournament.
Andrew Fifita shrugged off the attentions of Scott Grix five minutes later before Hayne wrapped the night off with his second try that Parker converted to bring up their half century.