Injury-ravaged Ireland became the first European team since 2003 to complete calendar-year victories over the southern hemisphere's big three by fending off Australia 27-24 in Dublin.
Ireland lost Rob Kearney, Andrew Trimble and Jared Payne to injury in a bruising contest, having entered the clash without Johnny Sexton and Robbie Henshaw and late withdrawal Sean O'Brien.
Iain Henderson, Garry Ringrose and Keith Earls claimed Ireland's tries, while Dane Haylett-Petty, Tevita Kuridrani and Sefanaia Naivalu crossed for the Wallabies.
Australia flanker Dean Mumm was fortunate to escape a red card for a dangerous tackle on Tadhg Furlong, while Bernard Foley was sin-binned late on for a challenge on Devin Toner.
Ireland wound up with replacement scrum-half Kieran Marmion on the wing and Joey Carbery at full-back, but still produced a stirring victory over the Wallabies.
Joe Schmidt's men shrugged off all their injury concerns to beat New Zealand, South Africa and Australia all in the same year - the first northern hemisphere side to complete the feat since England 13 years ago.
Ireland ripped into Australia from the off, but wasted three ideal platforms in the visitors' 22 after punting kickable penalties to the corner.
Some 17 Irish phases came and went on the move of the half that carried no reward, with Trimble hauled down just shy of the line.
Ireland had a penalty in the bag but Mumm - selected at six to disrupt the home lineout - did exactly that. Israel Folau then left a knee in on Kearney as he shipped out wide, effectively forcing Ireland's full-back out of the contest.
Kearney had only just beaten a concussion picked up in last week's 21-9 New Zealand loss, and was again withdrawn due to head injury checks here. Paddy Jackson slotted a penalty to put Ireland 3-0 to the good after Stephen Moore slipped off his feet at a ruck.
And then came the half's controversy. Mumm dumped Furlong at a ruck with Australia on the attack. The former Exeter back-five forward dropped Furlong on his head, however - and was hugely fortunate to avoid a red card.
Referee Jerome Garces explained "it's not a dynamic situation" to both captains in awarding Mumm a yellow card. An unfazed Ireland seized full advantage, Simon Zebo conjuring a try for Henderson thanks to a cute chip that Earls regathered.
Earls fed the onrushing Henderson inside and the Ulster lock sneaked his way across the line. Jackson's conversion had Ireland 10-0 ahead just into the second quarter.
Trimble was then forced off with ankle trouble, with Carbery slotting in at full-back and Zebo switching to the wing. Ireland fluffed a maul peel at the back of the lineout, only for Ringrose to scoop up the loose ball and wriggle home for the hosts' second try.
The stung Wallabies did however hit back. Rory Best produced a startling cover tackle on Reece Hodge to deny the visitors a score. Conor Murray dented another Wallabies raid, but Ireland could not keep Australia scoreless at the break.
Haylett-Petty finished courtesy of a neat inside ball from Folau as Michael Cheika's men left the tie neatly poised, with Ireland leading 17-7 at the break.
Ireland lost Payne at half-time, the influential centre suffering a back problem after having only just shaken off a "lower-limb tweak" to be fit for the clash.
Yet another backline reshuffle saw Earls shift to 13 and replacement scrum-half Marmion enter the fray on the wing. A forward pass from David Pocock denied Australia an immediate try at the top of the second half.
Just minutes later Kuridrani waltzed home however, with Ireland's backline at sixes and sevens. Jackson posted his second penalty of the night to nudge Ireland back into a 20-14 lead, but still Australia heaped on the pressure.
Replacement wing Naivalu coasted over with his first touch as Ireland lost their defensive shape, with Foley converting to hand the Wallabies a 21-20 lead.
A Foley penalty handed Australia a four-point advantage on the hour, but Ireland somehow found another gear. Earls raced in from Zebo's scoring pass thanks to bullish carries from CJ Stander, Furlong and Peter O'Mahony.
Jackson's nerveless conversion pushed Ireland back into a 27-24 lead. Ireland continued to hang in the match, and were handed a huge boost when Foley was sin-binned for a dangerous tackle on Toner.
The hosts then ground out the result, Jackson punting a full-time penalty into touch to spark raucous celebrations in Dublin.