Ireland, who opened up their challenge with a 22-10 victory over the USA, tackle the Wallabies at Eden Park, with the winner likely to top Pool C.
And the 32-year-old O'Driscoll is relishing the challenge of taking on the Tri-Nations champions.
"Games like these are huge and for me personally, knowing this will be my last World Cup, it's even bigger," he said.
"But as much as we know the enormity of the game, there's no point putting pressure on ourselves. We must still enjoy it.
"The occasion to shine is against the best teams in the world and Australia are ranked two in the world.
"Why not take the opportunity now, it might not present itself again? I'm excited about the prospect of taking Australia on.
"All of the hard work that I have put in over the last 10-12 weeks culminates in this. It's now or never, and hopefully it's now."
O'Driscoll has managed just three wins in 13 appearances against Australia - with the current class having potential to be a vintage.
However, O'Driscoll is confident his side can halt their charge.
"This is a very good Australia side," he added. "Any team that wins the Tri Nations is a force to be reckoned with. That speaks for itself.
"As a team you back yourself on the achievements you have and the medals in your pocket.
"Fresh in Australia's minds will be their victory in the Tri Nations and they have drawn confidence from that.
"But we must have belief in our own quality and on our day we feel we are capable of beating anyone.
"We have to make sure that our performance is up there with some of our best in recent years.
"We can't allow Australia to play and must impose ourselves on them."
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