On the field, Ireland rallied behind the bollocking front row of Cian Healy, Rory Best and the boulder-like Mike Ross.
The Australian scrum was repeatedly out-hit at the engagement and the entire Wallaby forward pack appeared stunned into submission.
The win in front of a bellowing 58,678 crowd consigns Australia to a likely meeting with the Springboks - with the winner almost certainly running into the All Blacks at the semifinals.
Michael McCulloch, 35, from Dublin, said: "That was unbelievable. It's probably the biggest upset in rugby for 20 years. I'm speechless."
Rebecca Powell, 32, from Tipperary, said: "We expected to come away as good losers. It's turned the whole tournament on its head. They didn't expect us to come at them like we did. It's going to be a messy one tonight."
Cathal Lennon, 28, from the Midlands, was delirious with joy. "We f***** beat them. I am euphoric. It's as good as beating the English. We were that good, at the end, even the Aussies were cheering for us."
Irishman Connor Irwin exploded out of Britomart rail station to head into Party Central with thousands of other Ireland supporters.
"To get it perfect like that, for me, to watch Ireland beat Australia at Eden Park was the best experience of my life. They pulled it out of the bag."
Kieran Hogan said: "It felt like they were playing in Ireland. It was brilliant."
Irishman John Savage called it Ireland's "biggest win".
"We beat the supposedly second-best team in the Rugby World Cup."
Accountant John Burke, 36, from Cork, currently lives in Sydney but stayed true to his home country, cheering Ireland to the win. "We witnessed history. We smashed them."
Australians in the crowd were dejected.
Former Wallaby hardman Sam Scott-Young said: "A tour group brought 200 people over and we will go back losers. In my opinion the Aussie players were tired and flat. They did not step up to the challenge of the passion of the Irish."
Former Wallaby prop Fletcher Dyson said the Australian scrum had been ineffective against the Irish. "They were going in too high."
He said it set up a tough ask for Australia to progress, with South Africa and the All Blacks standing in the way of a place in the final. "When Quade [Cooper] got the ball you could sense the Kiwis in the crowd. The booing was incredible."
Recruiter Tim Barnard, 35, from Sydney said "I'm devastated by tonight's game, absolutely devastated."
His mate David Royle, 34, a writer from Sydney, said: "I'd love five minutes with Robbie Deans."
Aucklander Daniel Pender said he supported Ireland because he hated the thought of rooting for Australia.
"Ireland's best-ever rugby result," Wayne O'Connor said.
