"We let ourselves down," admitted William Porterfield after Ireland stumbled to a deeply disappointing defeat in Colombo last night.

Australia's winning margin of seven wickets with 29 balls to spare in this Group B ICC World Twenty20 was a thumping in any language.

Aussie hero Shane Watson gave a clue to why Ireland were outclassed by a side that had clearly worked out plans to combat the Irish batsmen.

"Ireland are now in the challenging position of being well-known by the top teams", he said.

"Everyone knows they have highly-skilled players and that's not a surprise any more. The top teams now know they have to go full tilt against Ireland."

On a hot sticky day – 31 degrees and 90% humidity – Ireland looked to have blundered by spending 40 minutes warming up before the game, including their traditional game of tip rugby.

The Aussies are more used to playing in this part of the world and stuck to a few stretches and very light exercises – and were off in half the time.

Ireland also raised eyebrows by opting to bat, but the skipper explained his call by pointing to the excellent batting track.

Unfortunately for Porterfield, however, he didn't get the chance to find out how good it was, hooking the first ball of the day – from Watson – into the hands of Mitchell Starc at long leg.

It was his fourth golden duck of 2012 for Ireland – and second against Australia.

But as his previous first-ballers included the famous win over England, and the T20 final victory in Dubai in March, the omens remained positive.

However, Ireland's batting star Paul Stirling seemed rattled by the dismal start and was soon out for 7 after just one trademark boundary.

And while Ed Joyce hit some nice shots, including three fours, he was undone by Glenn Maxwell – and the humidity. The Sussex star's bat seemed to slip in his sweaty palms and he chipped the ball to mid-off.

"It was very frustrating as I felt so good", he said after the game, "the boys are devastated not to put on a better show but we'll be back for the Windies."

At 33-4 off seven overs, Ireland were facing a savaging, but the O'Brien brothers staged a good recovery.

With Niall content to work the ball around, Kevin played several thunderous drives and the pair rattled up their 50 partnership in 42 balls.

But Niall was yorked by Watson, and four balls later Kevin tried to lift the ball over the keeper but his connection was too thin and he was caught.

The Irish tail has been brittle in recent games, but yesterday they batted out their overs and a Nigel Jones six – Ireland's only maximum – in the last over brought the target over a-run-a-ball.

To have any hope the attack would need to cut the head off the Aussie order in quick time.

But Boyd Rankin and Trent Johnston were unable to threaten, and Watson and David Warner were soon in full flow.

Rankin had a nightmare second over, spraying the ball down leg-side, four of which were called wides.

And Johnston's second cost even more, with four boundaries coming in an over that went for 19.

The big YMCA man made amends with a sharp bit of fielding in the tenth over, throwing the ball to the far end and hitting the stumps to run out a dawdling Watson for 51.

And Kevin O'Brien trapped Mike Hussey in the same over to give Ireland a glimmer of hope.

But with fewer than 30 needed off nine overs it soon became a canter for Australia and Cameron White finished the game with a flourish.

With five days until they play West Indies, Phil Simmons has a big job to pick up his team if he wants that game not to be their last in this tournament.

• There was one small consolation for one Ireland fan – John Pryor from Malahide won a mobile phone as ‘Best Dressed Fan' in the Premadasa Stadium.