Australia's unexpected 3-2 loss to world No. 39 Chile could prove costly ahead of next month's 2019 Women's World Cup draw.
Australia completely dominated the first half at Penrith Stadium on Saturday but only had an early Emily van Egmond penalty to show for their advantage as busy Chile goalkeeper Christiane Endler remained a solid last line of defence.
Somehow, the South Americans went to the break level as Francisca Lara made the most of a moment of defensive chaos to finish from long range.
Chile's second sight of the net resulted in the second goal as Carla Guerrero steered an opportunistic effort home just after half time as Australia failed to deal with a free kick.
The Matildas uncharacteristically lost their way after falling behind. Chile substitute Yesenia Huenteo broke away to make it 3-1 in the final minute of injury time before Van Egmond struck her second penalty with the final kick of the match.
Australia, world No.6, need as many positive results as possible to secure a top-six seeding for the upcoming World Cup draw.
"That is out of our hands now, I think," coach Alen Stajcic said when asked about holding on to sixth in the rankings.
"All we can think about is improving for the next game and improving in every game from here on in."
The defeat was a rare blow for the Matildas, who hadn't lost in 11 matches at home, last against Brazil in early 2014. The team's form in the past two years and surge in popularity helped attract an record crowd of 15,185 at the Penrith Stadium.
"We certainly had control of the game," Stajcic said.
"They had three chances and they scored three, so that is disappointing. We gifted certainly two of them. That's international football and you pay for your errors. The clinical element probably went missing and once the scoreline went in their favour, we panicked a touch and lost that tempo that we had earlier."
The result sets up a fascinating second match in Newcastle on Tuesday.
Chile coach Jose Letelier admitted the win was unexpected.
"This is huge for women's football in Chile," he said.
"If you asked me before the game if we would have beat Australia, it would have been irresponsible to say yes, but sometimes football goes like that."