In perhaps the Matildas biggest match ever played, stand-in captain Steph Catley slotted the game winner from the spot in the absence of Sam Kerr, who was a late withdrawal after she sustained a calf injury at training the day before.
After Marissa Sheva brought down Hayley Raso in the box, the pressure fell on Catley in 52nd minute, but it didn't appear to phase her as she cooly dispatched the spot-kick. With no Kerr, the fullback was the natural choice; she scored Australia's lone penalty in their Round of 16 loss to Norway in 2019.
The Republic of Ireland refused to relent though, with goalkeeper Mackenzie Arnold forced to keep out a multitude of attacking raids on her goal for the final 20-minutes of the match.
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In front of a sold out, 75,784 strong crowd at Stadium Australia, the Matildas looked strong early, taking control from the opening whistle as they constantly pushed into Ireland's back third, repeatedly putting the defensive line under pressure, but the absence of Kerr saw a lack of finishing polish.
While Catley was rightly named Player of the Match for her match-winning effort, Katrina Gorry was everywhere for the Matildas, controlling the game from midfield, while Raso drew in Ireland's defence and won her side several penalties, including in the box.
In the end Catley's effort proved decisive as Ireland failed to break Australia's gold wall.
Rapid reaction
1. Foord-Fowler duo struggle to open up Ireland
The Matildas had to contend with the absence of Kerr up top and did so by injecting Mary Fowler into the front line.
While Kerr and Caitlin Foord have the ability to swap roles, playing both side-by-side and able to withdraw when needed -- a dynamic honed over four World Cups and countless matches together -- the same fluidity didn't translate to this pairing. More often than not, Foord played the role of the central striker while Fowler was tucked in behind as a No. 10, occupying the space between the lines. While this formation makes sense with the personnel available, and Fowler's specific strengths, it's a system which requires speed of movement. That becomes even more of a necessity when playing against a well-drilled defensive machine like Ireland and that is what the Matildas lacked in the first half.
Due to the slowness of the play, Fowler found herself in space but with no room for the pieces around her to click into place in order to make the most of that space.
The second half saw the Matildas quicken up their passing and decision-making. Rather than work around Ireland's defence once it had been set up, they could catch them out of shape and create much more threatening chances, and subsequently drawing what would be the match-winning penalty.
2. Gorry key for Australia
We're four years on from France 2019, but Katrina Gorry remains perhaps the most vital -- and underrated -- cog in the Matildas machine.
The 30-year-old set the tone on Thursday night, crunching into tackles just as often as she found herself dictating tempo with possession. Ever since Gustavsson re-introduced Gorry to heart of the Matildas midfield in early 2022 (alongside the tireless Kyra Cooney-Cross), Australia has looked far more balanced.
Gorry's talent has long been known by those Down Under. After this tournament the Queenslander may begin to get the international plaudits that she deserves.
3. Ireland leave empty handed despite strong performance
Ireland's World Cup debut ended in defeat but they more than held their own against one of the host nations.
The backline was immense in their handling of a Matildas attack that lacked Kerr but still had plenty of problems. In the first half in particular, they were able to keep Foord isolated and well covered. They were able to create chances up the other end as well and heaped on mountains of pressure.
The second half in particular saw the Irish tighten the screws as they searched for an equaliser -- and a first World Cup goal. They were relentless in their attack as they sensed Australia was happy to absorb pressure. Their set pieces put the Matildas defence on notice and a late charge in injury time had Australian hearts in mouths
In the end, Ireland never looked overawed by the occasion of a 75,000-strong, Australian record crowd in the stands and were incredibly well supported by large pockets of green and orange in amongst the gold.
Ireland boss Vera Pauw and her charges now turn their attention to another huge task: a trip out to Perth and a meeting with Canada.
Best and worst performers
BEST
Katrina Gorry, Australia: The 30-year-old midfielder was everywhere for the hosts against Ireland. From throwing herself into tackles to orchestrating attacks, it was yet another example of key Gorry is to the Matildas setup.
Steph Catley, Australia: If the pressure was on Australia's stand-in captain ahead of her spot-kick, she didn't show it. A coolly taken penalty was just what was needed on a nervy night for the hosts.
Mackenzie Arnold, Australia: Not under too pressure in the first half, Arnold was made to work hard in the final 20-minutes as Ireland upped the ante and sent what seemed like endless threats the goalkeepers way.
WORST
Marissa Sheva, Republic of Ireland: It's harsh on the 26-year-old, but giving away the penalty in a such a close match was always going to be pivotal.
Mary Fowler, Australia: Filling Sam Kerr's boots was always going to be a massive ask. Fowler had some quality touches but didn't see enough of the ball to have an effect on the match.
Highlights and notable moments
Key stats (provided by ESPN Stats & Information)
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