Sam Kerr, 25, has starred in the National Women's Soccer League since its establishment in 2013, claiming a second 'Golden Boot' award as the top scorer in 2018 after netting 16 times in 19 matches for Chicago Red Stars.
The U.S. squad features a number of her Chicago team mates, including midfielder Julie Ertz and defender Tierna Davidson, and other former colleagues at other clubs.
"It's a different experience ... In the change-room at Chicago there was a bit of banter going," said Kerr after the Matildas' final training on Wednesday.
"But there will be no friends tomorrow when we cross that line.
"And I guess if there is, you go harder on your friends than anyone else."
Australia, quarter-finalists at the last World Cup in Canada, are keen to benchmark their progress against the defending champions in the friendly ahead of the global showpiece in France starting in June.
The United States have a dominant winning record over the Australians but have been troubled by them in recent matches.
They were upset 1-0 by the Matildas at the 2017 Tournament of Nations and were held 1-1 in the same tournament last year.
Kerr said Australia had traditionally been guilty of worrying about the U.S. game more than their own, and that the team were more focused on developing for the World Cup rather than getting a result in Denver.
"It is a good benchmark but at the end of the day this is preparation for the World Cup," she said.
"We're going to be focusing on ourselves. We hope that we can win but the most important thing is continuing the journey to improve to get to the World Cup."
