Skipper gets Matildas home in Cup opener, but it wasn't Sam Kerr

But in this case it certainly was after left-back Steph Catley was given the armband for the Matildas after a bombshell dropped 90 minutes before kickoff with the news that captain Sam Kerr was set to start from the bench due to a calf injury sustained in training.

Read more: Watch the evolution of Caitlin Foord: from junior football hopeful to Matildas legend

In the end the Matildas still picked up an important 1-0 win to start their Cup campaign despite the Kerr injury, thanks to a converted penalty from Catley.

And after being frustrated by Ireland in the first half, Catley opened the scoring via the spot to send the Matildas on their way for three points in their World Cup opener at Homebush in front of 75,784 fans.

Speaking after the game, Catley said she was proud of the team's performance in the wake of Kerr's absence.

"We knew there would be nervy moments. It was probably the biggest game of our lives for all of us," she said.

"This has been the longest build up to a game in my entire life. We knew Ireland were going to be a massive task. But I'm really proud of the way that the team handled it.

"Sam is massive for us. For her as a person, we were completely heartbroken. But I think that we used the spirit and the fact that she wasn't able to be out there to help us push on.

"That's what it's going to take for as long as she misses," Catley added.

Kerr was seen in tears before the match on the pitch. She made the emotional news public on her social media pre-game.

"Unfortunately I sustained a calf injury yesterday in training," the statement read.

"I wanted to share this with everyone so there is no distraction from us doing what we came here to achieve. Of course I would have loved to have been out there tonight but I can't wait to be apart of this amazing journey which starts now."

She will also miss the next group game against Nigeria on July 27, where she will be assessed after that.

On the other hand, the visitors were given an injury boost with Denise O'Sullivan in the starting lineup after injuring her shin in the abandoned warm-up match with Columbia last week.

For Australia, a couple of former Illawarra Stingrays Caitlin Foord and Mary Fowler led the line up top in Kerr's absence.

And after all the hype, the game finally got underway. Australia had the most of the ball from the off, something that was expected before a ball was kicked.

It was a trend that continued for the entirety of the first half, with the team desperately missing Kerr up top. Foord in particular was marked out of the game in the first half.

Ireland - set up with a back three - were defensively sound and disciplined from the first minute.

The first half chance on goal came from Clare Hunt in her World Cup debut, with the defender coming up for a corner. She couldn't direct her header goal wards however.

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The Matildas had more of possession and the chances, but had to be weary at the back. They were nearly caught on the break in the 20^th minute but were saved by midfield pocket-rocket Katrina Gorry who won the ball as the last defender.

The tight spaces between the Irish defensive lines meant the Matildas were forced to go long at the back from centre-halves Hunt and Alanna Kennedy quite often, which was not proving effective for them and playing right into the visitor's hands.

The frustration was exemplified around the team, with Hayley Raso going down momentarily due to a clash of knees.

Katrina Gorry's late shot summed up the first half with a snapshot from distance that barely troubled the Irish goalkeeper Courtney Brosnan.

The half came to a close and there was plenty for coach Tony Gustavsson to discuss with his troops before the second 45.

Australia were awarded a golden chance to score the opener early in the second half however when Raso was brought down in the box by Marissa Sheva.

Foord originally had the ball in hand but handed it to her skipper Catley, who sent the goalkeeper the wrong way and made the score 1-0.

Warilla junior Foord attempted to double the scoring in her fourth Cup when she flicked on a header from a corner in the 68^th minute, but couldn't direct the ball on target.

There was a real heart in mouth moment for Australia at the back as Ireland searched for an equaliser. A Katie McCabe corner caused a lot of trouble for Mackenzie Arnold in goal, but the stopper was strong enough to swat the ball away.

But after some back and forth action in the closing stages where Ireland searched for that elusive goal, Australia hung on for a crucial three points and the 1-0 win.

Matildas coach Gustavsson said following the match that there were some nerves in the first half but the second half was much better.

"I have to credit the players for how they handled the final 15 minutes," he said.

"The way we defending set plays, especially our centre-backs was class. We had five World Cup debutants tonight. That says a lot. They proved that they can handle the pressure no matter the curveballs that are thrown at them."

The Matildas second game of the group is against Nigeria in Brisbane on Thursday July 27.