SYDNEY (AP) — How much of a role Sam Kerr can physically play for Australia at the Women's World Cup remains completely uncertain.

Even if her time on the sidelines with a calf muscle injury is extended, though, Australia's iconic striker still has important role to play for the tournament co-hosts after helping to inspire the Matildas to a 1-0 opening win over Ireland on Thursday.

“Obviously losing a player like Sam, probably the best player in the world, and just for her as a person, we were completely heartbroken,” said Steph Catley, who scored the 52nd-minute penalty that secured Australia's win in front of a record crowd. “We had to gather ourselves pretty quickly, but we used her spirit and used the fact that she wasn’t able to be out there with us to help us push on. And I think that’s what it’s going to take for as long as maybe she misses.”

Both host nations were in action on the opening day. The Australians were expected to have too much star power against Ireland, which was on debut at the tournament. New Zealand had never won a game at the World Cup.

But the New Zealanders produced a 1-0 upset win over 1995 champion Norway in the tournament's first match, hours after a fatal shooting in downtown Auckland shocked their nation. A minute’s silence was held before that match at Eden Park. A few hours later at Stadium Australia, a 75,784-strong crowd — a record for women's soccer match in Australia — also observed a minute of silence as a mark of respect before kick off.

A hush had gone over the crowd earlier than that when it was announced that Kerr, the highest-profile player in this part of the world, wouldn't be starting against Ireland.

She's also set to miss Australia's second Group B game against Nigeria next week and there are no guarantees she'll be back to take on Olympic champion Canada on July 31.

“She’s so, so important, she’s our spiritual leader and whatever role she plays in the next however long will be massive,” Catley said. “Sam was involved non-stop from the first chat in the changing rooms to the last chat. She was getting round everyone as you would expect.”

Without its captain and all-time leading scorer, Australia got over the line. Just.

Kerr has been the face of the Matildas’ bid to be crowned world champions for the first time. Without her leading the attack against Ireland, her teammates appeared short of ideas or cutting edge.

Then there was the psychological boost her absence provided Ireland, which was out to cause an upset in its first appearance at the World Cup.

Little wonder Australia coach Tony Gustavsson had tried to keep Kerr's injury a secret for as long as he could.

“I hope you respect and understand the reason that when I sat here yesterday I couldn't talk about it,” he said in a post-match interview. “But once we came to the stadium we didn’t play any type of mind games.

"We were honest. We got the team sheet. She wasn’t in the starting lineup. We went out with the news she was injured ... but we wanted to wait until the last second that we came to stadium to not give away too much.”

Without Kerr, it was down to Catley to convert the penalty that ended Ireland's resistance and sparked an eruption of joy from fans inside the stadium.

There was also no shortage of relief from the majority of the crowd.

When the chance came, it was a gift from Ireland shortly after the break when Marissa Sheva bundled Hayley Raso to the ground in the area.

Referee Edina Alves pointed to the penalty spot and Catley sent Ireland goalkeeper Courtney Brosnan the wrong way as she calmly finished with her left foot.

Sheva was in tears at the final whistle.

“It’s quite normal that you are upset after the game,” Ireland coach Vera Pauw said. “She will be fine. Anyone can make that mistake. Nobody blames her.”

Ireland had beaten Australia in the teams' last meeting, winning 3-2 in a friendly in Dublin in 2021.

And by the end Australia needed keeper Mackenzie Arnold to help hold off a series of late attacks in search of an equalizer.

Pauw said she was proud Ireland had “showed that we can play against the very best teams in the world.”

"We’ve now showed that against Sweden, against USA, now against Australia," she said. “The next one is against Canada the Olympic champion. We do not fear anyone and these players adapt so quickly.”

UP NEXT:

Australia plays Nigeria in Brisbane on July 27, a day after Ireland takes on Canada in Perth.

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James Robson is at https://twitter.com/jamesalanrobson

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More AP Women’s World Cup coverage: https://apnews.com/hub/fifa-womens-world-cup