Australia coach Mickey Arthur needs no reminding about the fairytale victories Ireland's cricketers have in their kit bag, like their one-day World Cup win over England in 2011 and their shock triumph over Pakistan in 2007.

Australia are unbackable favourites to win their opening World Twenty20 Group B clash with Ireland at Colombo's Premadasa Stadium on Wednesday (starting 2000 AEST).

But Arthur is taking no chances with his ninth-ranked side, who will come up against their former bowling coach Craig McDermott for the first time after the former Aussie Test spearhead switched to Ireland earlier this year.

"I know I'll only rest easy when that game's passed," Arthur said on Monday after his side's nine-run loss in a warm-up game against defending champions England.

"That's not through fear of failure. They have been a giant-killer down the line and they're playing with a quite nice bit of freedom at the moment.

"Any team in this competition can win if they have a good day."

Arthur played down the issue of what impact McDermott could have on the game's outcome.

"It doesn't uh, (pause), it doesn't really faze me," Arthur said.

"The coaches don't play the game. He could pass on all that info that he liked.

"It's like when hopefully we come up against South Africa deep in the tournament," added the former South Africa mentor.

"It doesn't make any difference. The players have still got to go out there.

"I'm just happy to see 'Bill' back on the circuit. It will be nice to catch up with him."

Arthur was not as carefree about Australia's bowlers coughing up 14 wides against England -- including eight from Mitchell Starc (2-32).

"Fourteen wides is not good enough. That's the difference between us chasing 159 and us ending up chasing 173," Arthur said.

"We're certainly not happy with that."

Star allrounder Shane Watson says the key to beating 10th-ranked Ireland is to play in ultra-aggressive style.

"Not too many guys have been talking about it but deep inside everyone knows they are a very dangerous team," Watson said.

"They've got some highly skilled players and we certainly have to be at our best to make sure we dominate the game."