The visitors are missing their four best players in Melbourne this week, with Emma Raducanu, Francesca Jones and Katie Boulter opting to focus on the European clay-court swing.
British No. 2 Sonay Kartal is unavailable after she injured her back at Indian Wells last month.
It means 17-year-old debutant Mika Stojsavljevic, ranked 275th in the world, will kick off the best-of-five-rubber format against Australia's in-form Talia Gibson at John Cain Arena on Friday.
"It's a real privilege to be in the (BJK Cup) side and it can absolutely bring out the best in you," Australia captain Stosur said.
"But you certainly can't think that there's a huge favourite at all because funky things have happened with results over the years.
"It's something that hopefully goes our way this time and these guys play the best they've ever played and we walk off feeling happy."
World No.173 Harriet Dart will also feature in singles for Great Britain, taking on Kimberly Birrell (80th) in Friday's second match.
Dart will then partner Jodie Burrage in Saturday's live doubles match against experienced Australian duo Storm Hunter and Ellen Perez, with the reverse singles scheduled later in the day.
"Absolutely we are the underdogs on paper, but we thrive in this competition and in the past we've been able to cause big upsets," Great Britain captain Anne Keothavong said.
"It's a different type of feel and pressure for all the players representing your country and I know the players we have up here take a huge amount of pride in it.
"We've prepared well and all I can ask of the players is to go out there and give it your best shot because we're all right behind you.
"There's nothing more to add to that, but the pressure is all on the Aussies and the expectations, I have no doubt, that you'll put on them will be high, which is fine for us."
Gibson spearheads Australia's charge after a back injury forced world No.30 Maya Joint's withdrawal.
The 21-year-old last month became the youngest player in seven years to reach a quarter-final in her WTA 1000 debut.
It capped a whirlwind run in which she beat five top 20-ranked players and rocketed to her career-high ranking, climbing from No.119 since January.
"It's still a little bit of a shock to me that I'm now in this position after the last month and how I (performed) in the US," Gibson said.
"I'll take confidence from that and know that I belong in this position and I've earned it.
"I'm really proud of how I've been playing and the work that I've been putting in, so when I go out I just want to enjoy that moment."
The winner of the tie will advance to the eight-nation Finals, scheduled for September in China.
Australia won seven of the first competition's first 12 stagings but have not done so since Evonne Goolagong-Cawley led them to success in 1974 in what was then known as the Federation Cup.
Since then, Australia have reached the final 10 times without making the final step.
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