In turning the form book on its head in Auckland, Brian O'Driscoll and his team-mates not only restored Irish faith — both within the squad and among supporters — but also took this predictable World Cup in a whole new direction.
The apparent certainty of an all-Antipodean final at Eden Park on October 23 is now effectively dead and buried. It could still happen but would require an extraordinary set of results to make what appeared the seemingly inevitable now occur.
Ireland beating Australia marks the first big upheaval of this World Cup and follows on from Wales' gallant effort when losing to South Africa by a single point in a match they should have won.
Does it mean the tide is turning the northern hemisphere's way? Not a bit of it — the big southern hemisphere three are still leading the way, but on any given day any of the Six Nations teams are well capable of putting it up to the Kiwis, Springboks and Wallabies.
The difference last Saturday was that Ireland closed it out and with the type of conviction that will have the Tri-Nations teams preparing like never before for possible bushwhacking.
The flip side of that coin from an Irish perspective is that confidence has been restored. The trick now is to keep a lid on self-belief — a modicum of doubt in the camp is never a bad thing. That sickly feeling of maybe letting yourself, your team-mates and your country down must never be removed entirely in the build-up to any game.
The challenge for any head coach is in striking the proper balance and there is no one better than Declan Kidney in getting that aspect right. After this morning's Italy versus Russia clash, every team is now at the halfway point in their respective pools and it looks like a very definite change in trend towards the knockout phase.
Ireland still have much to do — particularly against the Italians — to top the pool, but we are now in charge of our own destiny. Whereas the Australians had mapped their route (in avoiding South Africa and New Zealand) towards a fourth World Cup final, it now appears as if the Tri-Nations teams will be in a shoot-out (along with the winner of Scotland versus Argentina), which leaves England, Ireland, France and Wales to battle it out in the other half of the draw. All of which points to a sixth north v south final in the seven tournaments to date.
While only England (in 2003) have arrested southern hemisphere domination, the gap is nowhere near as great as some would have you believe. I still feel this tournament is New Zealand's to lose, but don't write off the Boks who, though extremely limited in ambition, have the essential components to suffocate any team in a one-off match — the All Blacks included.
As for Ireland, we are now the adopted team of the host nation. By putting the Wallabies to the sword we became every Kiwi's second favourite team.
However, we have also just channelled Australia into a potential semi-final showdown with the All Blacks, something they might not exactly thank us for. Either way, Ireland's victory and the manner of it has given everyone (Australians apart) a massive boost.
As for Cian Healy, Rory Best and Mike Ross, their combination (particularly at scrum time) represents an Irish side transformed and proof positive of the significance the set-piece still has in the modern game. And there is the boost to collective morale the victory over the Aussies and the timing of it will have had.
A new era hasn't begun in Auckland but an experienced one with buckets of hunger has been resurrected.