Steph Catley scored the only goal from the penalty spot for the Aussies.
The Republic of Ireland suffered a narrow 1-0 defeat to Australia in their first ever Women's World Cup game.
A 52nd minute penalty converted by Steph Catley was the difference between the two sides in Sydney after a foul by Marissa Sheva.
Ballinasloe's Heather Payne played the full 90 minutes for Vera Pauw's side.
Earlier, co-hosts New Zealand caused a huge upset in the tournament's opening game.
Hannah Wilkinson's goal gave the co-hosts a 1-0 victory over Norway in Auckland, their first-ever World Cup win in 16 attempts.
Our team 🇮🇪
— Ireland Football ⚽️🇮🇪 (@IrelandFootball) July 20, 2023
10' | Ireland have settled well in a fantastic atmosphere as the Fields of Athenry rings around the stadium for the first time {0-0}#COYGIG | #FIFAWWC pic.twitter.com/ltegHqWwCE
75,784 people filled Stadium Australia in Sydney, with thousands of them Irish fans.
The record is still held by a Barcelona/Wolfsburg match last year, when 91,648 people turned out.
A minute's silence was held ahead of both fixtures after a deadly shooting in Auckland.
Two people were killed close to the Norwegian team hotel.
Ireland's next game will be against reining Olympic champions Canada next Wednesday with a 1:00pm kick off Irish time.
Australia top Group B while group opponents Canada and Nigeria - meet in the morning.
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