The United States and Greece are favoured to advance to the final as the inaugural United Cup mixed teams tennis tournament reaches the pointy end in Sydney.
The US play Poland and Greece face Italy in two intriguing semi-finals featuring several Australian Open title contenders at Ken Rosewall Arena on Friday.
Top-ranked Iga Swiatek takes on American world No.3 Jessica Pegula in an opening rubber that shapes as pivotal, particularly for Poland.
The Poles will be sweating on Swiatek keeping her unbeaten singles record for the week intact ahead of the first men's match between US Open semi-finalist Frances Tiafoe and the lowly ranked Daniel Michalski.
A loss to Pegula, who is undefeated in both singles and mixed in four matches this campaign, would leave Michalski needing to cause a huge boilover to save Poland from falling behind 2-0 ahead of Saturday's second singles rubbers and the mixed.
World No.9 Taylor Fritz will play 10th-ranked Hubert Hurkacz in Saturday's opening match, before 2022 Australian Open semi-finalist Madison Keys meets Magda Linette.
The clash between Greece and Italy also shapes as a tight affair.
In top-10 stars Stefanos Tsitsipas and Maria Sakkari, the Greeks look to have the edge ahead of singles tussles with Matteo Berrettini and Martina Trevisan.
Greece had to make the long flight across the country to Sydney on Thursday's "rest" day after Tsitsipas and Sakkari starred in Wednesday night's thrilling 3-2 win over Croatia in the Perth City final.
Tsitsipas and Sakkari won their respective singles matches, then beat Petra Martic and Borna Gojo 7-6 (8-6) 6-4 in the deciding mixed doubles.
"I'm proud of the team. Fighters is what defines us," Tsitsipas said.
"The first big step we took here in Perth is going to be memorable."
Sakkari, who won her singles match 6-3 6-3 against Martic, felt her doubles combination with Tsitsipas was continuing to flourish.
"I'm so happy and proud of this team," said the world No.6.
"Our games are clicking and we know each other really well, and we have a great chemistry on the court, and that's the key."
The semi-finals conclude on Saturday.
