Ireland signed off from their Grand Slam season with one last high as they edged a tense decider 20-16 in Sydney to claim a first series win in Australia since 1979.
A record 44,085 crowd packed into Allianz Stadium for its final Test match, but there was no fond farewell for the Wallabies, who could not make their late pressure pay as Ireland hung on desperately at the end of a long campaign.
They have had more impressive wins in 2017/18, but this one was all guts as they tackled their hearts out, struck through a CJ Stander maul try and clung on for dear life.
Referee Pascal Gauzere and his television match official Ben Skeen were central figures until the death, reviewing the last play several times before deciding that Jacob Stockdale was not guilty of deflecting Bernard Foley's pass before it flew into touch.
At the end of three absorbing games, it was a cliff-hanger finish.
Ireland started by taking the lead after eight minutes as Johnny Sexton punished Adam Coleman not rolling away.
But, after a quiet 80 minutes in Melbourne, Israel Folau was determined to have an influence and he claimed a second spectacular restart, allowing Kurtley Beale to chip in behind where Rob Kearney carried the ball over his own line and then put a foot in touch.
Australia's initial attack came up short, but an Irish offside handed Foley the chance to level.
A promising Ireland move came to an abrupt end when David Pocock got over the ball, but the Wallabies suffered a big blow when captain Michael Hooper suffered a hamstring injury and was forced off.
A high fend from winger Stockdale drew the attention of Skeen and Gauzere opted for a yellow card for the youngster. Foley further punished the offence with a fine penalty to put his side in front.
Sexton equalised after Pete Samu played Conor Murray off the ball and, just as Stockdale returned with no damage done, Australia lost Folau for 10 minutes for playing Peter O'Mahony in the air off the kick-off.
The Ireland captain joined his opposite number off the pitch, but the team were not deterred and Sexton nudged his side in front after another set of phases came to nothing.
Foley levelled, but Kearney's pressure forced Dane Haylett-Petty to knock Sexton's well-judged kick-off on and, when Samu Kerevi picked the ball up in an offside position, the Ireland out-half made it 12-9 at the break.
Ireland went for the jugular in the minutes after half-time, turning down successive penalties to go to the corner and they got their reward at the second attempt as they mauled their way over for Stander to touch down.
Sexton missed a kickable conversion and Ireland led by eight, but they immediately came under pressure after conceding a scrum penalty in front of their own posts.
Australia went to the corner and, while Folau knocked on with he line beckoning, a Murray off-side handed them another shot and this time they went through 13 phases before Foley's delicate chip popped up for Marika Koroibete, who powered through Kearney and Sexton to score.
Foley made it a one-point game and with all of the momentum behind them and their front-row replacements making a huge impact the Wallabies piled pressure on, but Foley missed a chance to put them in front from the touchline.
A Kerevi line break came to nothing when Foley knocked on, but Ireland were hanging on by their finger-tips.
But when Tolu Latu was penalised for not releasing the tackler a fatigued Sexton nailed a tough penalty to stretch the lead to four.
Folau superbly claimed the restart and, with less than a minute remaining, the home side went searching for a winning try. Folau surged forward and Foley looked to find the men on his shoulder, but his pass flew into touch.
For one last time, referee Gauzere went to the television match official to investigate whether Stockdale had touched the ball and, after several slow-motion replays, they decided there was no clear evidence of an offence.
Ireland celebrated wildly at the whistle, Australia looked stunned and the home fans booed as a memorable series proved dramatic until the death.