Quade Cooper admitted the Wallabies were in a state of shock after an inspired Ireland turned the Rugby World Cup draw upside down with a famous victory over the Wallabies on Saturday night.

Ireland decimated injury-hit Australia at the set piece to stun the Wallabies 15-6 in Auckland and leave the Tri Nations champions facing a horror draw in the knockout stages.

Second-ranked Australia will likely need to conquer defending champions South Africa in the quarter-finals and then tournament favourites New Zealand in the semis just to make the championship decider on October 23.

"The road that we have from here on in is a tough road but one that everyone's up for," Cooper told AAP.

"This sort of game makes you realise this tournament only comes around every four years and losing one game can be detrimental to the rest of the tournament.

"But we're in a good position that this one game isn't the end of the road for us.

"It just makes the road a little bit more tougher."

Skipper James Horwill conceded Australia's dressing room was "not a happy place to be at the moment", while Cooper said the Wallabies were shellshocked.

"It's never a good feeling when you lose a game, especially when it's an important game in an important competition like the World Cup," Cooper said.

"So there's a point where you've got to say 'we messed up there and as a team we've got to do better'.

"We've got to be in and amongst it around the finals series. We've got to get better and we've got to improve next week (against the USA)."

Australia were unable to overcome the match-day loss of champion flanker David Pocock (back) and hooker Stephen Moore (stomach bug) as Ireland ground out a bruising victory with an utterly dominant forwards display.

Australia's scrum suffered terribly, penalised five times for collapsing, evoking painful memories of the Wallabies' shock quarter-final exit at the last World Cup in France in 2007.

Just as England's Johnny Wilkinson did four years ago in Marseilles, Ireland punished Australia for their set-piece deficiencies, with five-eighths Jonathan Sexton and second-half replacement Ronan O'Gara each slotting two penalty goals.

Sexton also nailed an early drop goal as the two sides went to halftime locked up at 6-all.

The defeat left Australia on a quarter-final collision course with South Africa, who roared back to life with a 49-3 thrashing of Fiji earlier on Saturday.

Presuming they account for the USA next week in Wellington, then Russia in Nelson and negotiate a way past the Springboks, the Wallabies would almost certainly run into the All Blacks in the semi-finals.

The loss was also just Australia's second in a pool stage at a World Cup after also falling to South Africa 27-18 in 1995.

It also extended Australia's misery at Eden Park, with the Wallabies' last Test triumph at the ground coming back in 1986 - a quarter of a century ago.

"Ireland were very effective in denying us momentum," Wallabies coach Robbie Deans said.

"They defended very well and didn't allow us to recycle ball and it was effective.

"We would have liked more field position but our decision-making wasn't always great and, when we did get momentum and we did get behind them, we were impatient and we let the pressure off."

The long-overdue victory for Ireland was payback for four losses to Australia at previous World Cups, the most shattering a last-ditch 17-16 quarter-final defeat in Dublin in 1991.

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