Ireland captain William Porterfield won the toss and elected to bat first, but it could not have started worse for him or his side as he departed for a first-ball diamond duck.
Australia restricted their opponents - ranked just one spot below them in 10th in the world rankings - to a meagre 123 for seven from their 20 overs.
George Bailey's side cruised to their total with 29 balls to spare as they ended on 125 for three, with Shane Watson starring with bat and ball, as Ireland were left bitterly disappointed with their collective performance.
Man-of-the-match Watson took three for 26 from his four overs as he opened with the new ball, before clubbing 51 runs off 30 balls as he led the way with the bat.
"It wasn't as much a wicket-ball I suppose, but it just worked out luckily enough," Watson said of his first-ball dismissal of Porterfield before going on to suggest he may not bowl the first over in subsequent matches.
"It was a blueprint for this game and I am not exactly sure that is going to absolutely continue."
Ireland's Ed Joyce got a start with three impressive boundaries at the start of his innings following the loss of Porterfield, but he departed for 16 with opener Paul Stirling also going early for seven - caught by Watson off the bowling of Mitchell Starc.
Watson added the key wickets of Niall O'Brien and the dangerous Kevin O'Brien, while the impressive fast bowler Starc finishing with two for 20 from his four overs.
"Stirling is a quality hitter of the ball. So we knew that was a very important wicket, as well as (the wicket of) Kevin O'Brien," Watson said.
Kevin O'Brien top-scored with 35 from 29 balls, but after he and his brother Niall both departed in one potent over from Watson Australia always had the match in control.
"If we had come up with an extra 40-45 runs it would have given us a chance," Porterfield said.
Warner bludgeoned four boundaries as he accompanied Watson to a 60-run opening partnership before he holed out attempting to hit spinner George Dockrell for a maximum.
With the run-chase having been given a solid opening platform, Watson ran himself out just after reaching his half-century off 30 balls and was unable to lead his side to victory.
It was left to Cameron White and skipper Bailey to steer their side to the required total, with the number four finding the midwicket boundary to end the contest with a flourish.
Australia could not have wished for a more comfortable start to their campaign against an Irish side who promised a lot more than they were able to deliver on what was a good wicket in Colombo.
Tournament favourites India beat Afghanistan by 23 runs in their opening Group A encounter at the Premadasa Stadium later on Wednesday.
England are the third team in Group A, and begin their campaign against Afghanistan on Friday.