For Australia and USA, the stakes could not be higher and their task could not be clearer.

Win in Kashima on Tuesday and a place in the last eight will be assured. Lose and they will dicing with Olympic elimination.

The outcome of key individual battles will, as always, go a long way to determining the outcome, and few of tomorrow’s duels carry the intrigue or importance of Sam Kerr versus Alyssa Naeher.

As a showdown between, arguably, the best striker and goalkeeper on the planet, it would have been pivotal even without a wider context or personal connection. But it just so happens that Kerr and Naeher know each other very well indeed.

The pair enjoyed two years playing together with Chicago Red Stars, during which Kerr smashed all manner of NWSL records and Naeher nailed down her spot as USA’s No1. And as their careers blossomed, so too did a strong and enduring mutual respect.

“For me, she’s probably the best keeper in the world,” Kerr told FIFA.com. “But besides being an unbelievable player, she’s an even better person.

“I’ve actually not met Alyssa in a while, so it will be really nice to see her again. I just hope she’s not too happy when we say goodbye!”

Naeher’s mood is sure to be largely dictated by whether she has kept out her old friend, and that, she acknowledges, tends to be easier said than done.

“Sam’s an absolutely phenomenal player,” enthused the US World Cup winner. “A class striker and a class person – one of the good ones for sure. I have so much respect for her.

“Friendship aside, she is - and has been for several years - one of the very best in the world. It will be a great challenge to face her.

“We’re going to need to be aware of where she is at all times because she’s athletic, great in the air, can get you in behind – she’s so good at scoring in so many different ways. As a defence, we just need to stay switched on and do what we can to shut her down. If we don’t, there’s no doubt she will hurt us.”

Naeher speaks from experience of not only playing with Kerr, but against her - for club, country and, of course, in training. It seemed fair to ask each of them, therefore: who tended to come out on top in their one-on-one battles?

“Ah, I’m pretty sure I always beat her,” said Kerr, laughing. “I’m sure she’d tell you the same!”

“I don’t know about that,” responded Naeher, “but I’ll give Sam this: she always had better banter than me (laughs). We had a good back and forth in those days and, joking aside, I think we really helped each other. Training with quality strikers has definitely made me a better goalkeeper, and I like to think I maybe helped her improve too.”

Naeher can be safe in making such an assumption, and she is not the only American star who helped take Kerr’s game to a new level in Chicago.

Julie Ertz was another of the Aussie’s Red Stars team-mates, and the defender-turned-midfielder’s influence on USA was demonstrated again by the change she helped effect on her return to the world champions’ line-up.

“She’s a huge player for us, and everyone knows we miss her presence when she’s not there,” said Naeher, speaking in the wake of Saturday’s 6-1 demolition of New Zealand. “It was great to have her back, and the fact she managed 90 minutes is a big boost for us.”

“One of the toughest and best out there,” was Kerr's verdict. “I’m definitely happier when Julie’s on my team than when she’s playing against me, that’s for sure. Anyone in the game will tell you the same. She’s phenomenal.”

The same, in truth, could be said of all three of these old friends ahead of their Red Stars reunion. The question now: which of them will be left celebrating after Chicagoan sparks fly in Kashima?