With two days of United Cup group play remaining, two of the quarterfinalists in Perth have been determined -- Poland, led by World No.1 Iga Swiatek and Hubert Hurkacz -- and the home team, Australia.

Meanwhile in Sydney, with Groups B, D and F, nothing has been settled.

Six teams are in action Tuesday -- Greece, Czech Republic, Serbia, Chile, Croatia, Netherlands. The 1-0 Dutch squad can clinch the top spot in Group F with a win over Croatia in Sydney, while 1-0 Serbia can advance with a win over the Czech Republic in Perth.

For Greece, with singles players Maria Sakkari and Stefanos Tsitsipas, it’s the first time out in a matchup with Chile. And while Sakkari and Tsitsipas are stellar singles players, it could well be their doubles skills that carry them. As the top seeds in the 2023 United Cup, they played mixed doubles three times -- and were undefeated against Bulgaria, Belgium and Croatia on the way to the semifinals.

With the new best-of-three format, mixed doubles is more crucial than ever. In the first four days of competition a remarkable 10 of 13 results were determined by the final mixed doubles match.

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Taylor Fritz of the United States saw it coming.

“I just think we’re going to see a lot more matches come down to the mixed doubles,” he said before the event, “and that’s something that not a lot of the players I guess have a lot of experience in. So, the pressure is going to show in those moments and it’s going to make for some really exciting matches.”

He wasn’t kidding. On Sunday, Fritz and Jessica Pegula prevailed 10-7 in a third-set tiebreak over Katie Boulter and Neal Skupski to edge Great Britain 2-1. On Monday, all four ties came down to mixed doubles.

United Cup: Scores | Order of play | Draw

Maybe that’s why they call it the United Cup.

Here’s what’s on tap across three events in four busy arenas in Australia and New Zealand:

Auckland

While the United Cup is lighting up the courts in Perth and Sydney and the Brisbane International features a loaded draw, don’t sleep on the quality on display across the Tasman Sea at Auckland’s ASB Classic.

For starters, there’s No.2 seed Elina Svitolina versus Caroline Wozniacki, two heavily decorated mothers who returned to the Hologic WTA Tour last year. Svitolina played most of the season, winning the title in Strasbourg and reaching the quarterfinals at Roland Garros and the semifinals at Wimbledon.

After more than three-and-a-half years away, Wozniacki played only seven matches in 2023 but reached the fourth round of the US Open. The 33-year-old won the 2018 Australian Open title.

Svitolina, four years younger, holds a 4-1 head-to-head advantage, but the last time they played was the 2018 WTA Finals.

Whoever prevails gets the winner of Emma Raducanu against qualifier Elena-Gabriela Ruse. 2021 US Open champion Raducanu, coming off three surgeries, has been away from tennis for more than eight months.

The top seed is World No.3 Coco Gauff, who takes on Claire Liu on Tuesday. They’ve played once, at 2022 Indian Wells, with Gauff winning in straight sets.

Brisbane

Two Grand Slam champions are in play Tuesday, with No.8 seed Victoria Azarenka versus Anna Kalinskaya and No.14 Sofia Kenin against Arina Rodionova.

United Cup: Sydney

Having two Top 10 players is a wonderful learning opportunity for the four other players on Team Greece who are not.

“For us, they’re big examples,” Despina Papamichail said. “We follow them all the year, like we’re looking forward to be playing with them, with Maria [Sakkari] in Billie Jean King Cup and Stefanos [Tsitsipas] in United Cup, which is a great opportunity for us to learn from them.

“They opened the doors and showed the way. We are trying to follow.”

Valentini Grammatikopoulou concurred.

“It’s a big gift for us to learn from these guys who are top, Stefanos and Maria,” she said. “It’s a big boost for the whole year to learn how they fight and the support they give us.”

Sakkari lost her three matches at the WTA Finals in Cancun but finished among the Top 10 for the third consecutive year. She draws Daniela Seguel in a first-time meeting.

For Croatia, Donna Vekic takes on the Netherlands' (1-0) Arantxa Rus. Vekic won both of their previous matches.

Schedule of play

Not before 10:30 a.m. in Sydney

  • Maria Sakkari (Greece) vs. Daniela Seguel (Chile)
  • Stefanos Tsitsipas (Greece) vs. Nicolas Jarry (Chile)
  • M. Sakkari / S. Tsitsipas (Greece) vs. D. Seguel / N. Jarry (Chile)

Not before 5:30 p.m.

  • Borna Coric (Croatia) vs. Tallon Griekspoor (Netherlands)

Not before 7 p.m.

  • Donna Vekic (Croatia) vs. Arantxa Rus (Netherlands)
  • D. Vekic / I. Dodig (Croatia) vs. D. Schuurs / W. Koolhof (Netherlands)

United Cup: Perth

One of those mixed doubles deciders came on New Year’s Eve in Perth, when Novak Djokovic and Olga Danilovic defeated Zhang Zhizhen and Zheng Qinwen 6-4, 1-6, [10-6].

It was an over-the-top, bucket-list moment for Danilovic.

“When he did the volley, when the match was finished, so many emotions [going] through me,” she said. “Just feeling proud of myself. It’s my first time playing mixed, first time with Novak. I think it was one of the best moments in my career.”

Serbia (1-0) closes out its Group E play against the Czech Republic (0-1), with Danilovic playing reigning Wimbledon champion Marketa Vondrousova. The two have never met.

Vondrousova lost her opening match to Zheng, but if the Czechs manage to beat Serbia all three teams will finish 1-1.

Schedule of play

Not before 10 a.m.

  • Marketa Vondrousova (Czech Republic) vs. Olga Danilovic (Serbia)
  • Jiri Lehecka (Czech Republic) vs. Novak Djokovic (Serbia)
  • M. Kolodziejova / P. Nouza (Czech Republic) vs. O. Danilovic / N. Djokovic (Serbia)