Bench power proves the difference for Ireland as second half surge gets World Cup off to a winning start
Ireland 19 Australia 17
It was never going to be a perfect performance but the manner in which Ireland dug deep to keep their World Cup dream alive could well prove to be the kind of victory that propels this team to where they want to get to.
They showed flashes of their quality but couldn't find a way to shake off a stubborn Australia side who refused to lie down.
Having opened up a nine-point lead in the latter stages, it looked like the hosts had finally pulled away but a late Australia try made for a nervy finish.
It sets Ireland up perfectly for Sunday's clash against Japan before taking on France next week in what is likely to be a pool decider.
Tries from Larissa Muldoon and replacements Ciara Griffin and Sophie Spence, who both made a massive impact from the bench, ensured that the packed home crowd were treated to a cracking spectacle that ultimately ended in the result that they had all come to see.
Led by a towering display from man-of-the-match Maz Reilly in the engine room, Ireland's superior set-piece was crucial. There is plenty for Tom Tieney to work on before Sunday but Ireland will grow into this tournament as it goes on. Last night was about one thing: winning.
Jenny Murphy typically set the tempo in defence as she put in two huge hits early on but the centre was being called upon far too often as Ireland struggled to get out of their own half.
It took a brilliant Reilly lineout steal to relieve some of the early pressure but it was still 15 minutes before Ireland ventured into Australia's 22.
Reilly won her 50th cap in the Grand Slam decider against England in March and her experience was key, She would steal another two Australian throws in what was a hugely impressive performance.
After 19 minutes, Reilly, the tallest player in the tournament at 6ft 3in, again rose highest to claim the lineout, this time off Ireland ball, and a training ground move worked to perfection as the powerful rolling maul drove Australia close to their own line.
The ball was eventually worked wide and after Murphy and Ailis Egan carried well through the middle, a gap opened up and Muldoon didn't need a second invitation to dive over the white wash.
Nora Stapleton composed herself after a nervy start to add the extras as Ireland opened up a 7-0 lead after soaking up a barrage of early pressure.
It was just the start Tierney would have been demanding from his side but he will have been furious with the manner in which they went to asleep nine minutes later.
Australia took a quick lineout and just as Ireland's plan had worked earlier, the visitors' did too as they put plenty of width on the ball which allowed Mahalia Murphy step inside Eimear Considine and score.
Samantha Treherne lined up the conversion but was unlucky to see the ball fall off the tee just as she was about to strike it. It was a wake up call for Ireland and it stunned the 3,500 sell out crowd at the UCD Bowl into silence.
Fittingly, with the first half drawing to a close, Reilly's third steal brought an end to more Aussie pressure as Ireland held on to their slender 7-5 lead at the break.
Murphy appeared to pick up an injury making a trademark big hit in the first half and she only lasted seven minutes of the second in what was a huge blow for Ireland.
The hosts were again on the back foot but their aggression in defence repelled the wave after wave of gold attacks.
Ireland needed a lift and Sophie Spence provided that from the bench after 51 minutes. The substitution brought the crowd to their feet but four minutes later they were sitting back down again as Australis struck for a second try that proved to reignite Ireland's challenge.
They patiently went through the phases before captain Shannon Parry who won a gold medal in sevens at the Rio Olympics last year crashed over.
Treherne was again of target with the conversion but her side still took the lead (10-7) for the first time in the game after 55 minutes.
Ireland's response however was emphatic. Griffin's introduction might not have been greeted with the same noise as Spence but when she forced her way over the line under the posts three minutes after coming on, the boisterous home crowd were sent into raptures.
Miller linked brilliantly with Hannah Tyrrell down the right flank and suddenly the Aussie defence was scrambling. Ireland continued to hammer away around the fringes before Griffin dotted down. Stapleton's conversion put Ireland back into a 14-10 half time lead with 18 minutes left on the clock.
Ireland's bench were having a telling impact with Spence and Griffin adding plenty of ballast up front. It was their side's turn to dominate possession and unlike their opponents, they were able to make it fully count on the scoreboard.
Australia tired and no answer to Ireland's power and when Spence got over for a second try in nine minutes, there was daylight between the sides for the first time.
But Ireland again took their eye off the ball and Australia went straight down the other end of the pitch and scored a try through Hilisha Samoa that Ashleigh Hewson converted.
The gap was now back to two points as the clock ticked into the 75th minute but the time was not going fast enough for Ireland.
But the hosts showed great character to cling on to a precious victory that keeps their World Cup dream alive.
Ireland - H Tyrrell; E Considine, J Murphy (K Fitzhenry 47), S Naoupu, A Miller; N Stapleton, L Muldoon; L Peat, C Moloney, A Egan (C O'Connor 51); P Fitzpatrick (S Spence 51), M-L Reilly; A Baxter, C Molloy (capt), H O'Brien (C Griffin 58).
Australia - S Treherne; N Masters (A Hewson 70), K Sauvao (S Riordan 71), S Williams, M Murphy; T Pomare, K Barker; L Patu (H Ngaha 71), C Campbell, H Samoa; C Butler, M Boyle (R Clough 16-28, h-t); M Gray, S Parry (capt), G Hamilton.
REF - T Barker (Hong Kong)