Katie Boulter and Charles Broom sealed the win for Great Britain with a 7-6 (7-4) 7-5 triumph over Maria Carle and Tomas Etcheverry in a one hour and 45-minute deciding match at Sydney's Ken Rosewall Arena on Monday.
Etcheverry had squared the ledger with a comeback 6-3 3-6 2-6 win over Billy Harris after Boulter won the women's singles 6-2 6-3 against Nadia Podoroska.
Katie Boulter impressed in winning the opening singles against Nadia Podoroska. (Mick Tsikas/AAP PHOTOS)
Australia, after suffering a 2-1 loss to Argentina in their opening tie, can progress to the quarter-finals if they beat Great Britain on New Year's day.
At Perth's RAC Arena, Kazakhstan locked in a spot in the quarter-finals after defeating Greece in both singles matches.
Greek star Stefanos Tsitsipas fell first, beaten 6-4 7-6 (7-0) by Alexander Shevchenko.
Teams across Sydney and Perth who don't finish at the top of their group can also progress if they are the best runner-up team out of the three groups in either city.
Boulter and Broom bringing the 🔥 power for Great Britain 🇬🇧— United Cup (@UnitedCupTennis) #UnitedCup | @the_LTA pic.twitter.com/PgyCcVyyIrDecember 30, 2024
Boulter gave Great Britain the ideal start with her easy win over Podoroska in 86 minutes, seemingly enjoying a home-crowd advantage as fiance Alex de Minaur watched in the stands.
She announced her engagement to the Australian No.1 on Christmas eve after almost four years of publicly dating.
"We did them (Australia) a favour today giving them a 2-1 win so they can thank us later for that," Boulter said.
"We've got everything to play for. I'm going to come in all blazing."
The 28-year-old is unlikely to come face-to-face with de Minaur in the mixed doubles on New Year's day, with Matt Ebden and Ellen Perez having combined for the Australian team.
"I don't know about having a little match against him," Boulter said.
"I think that's going to be terrible and a bit of a popcorn match."
It is the second year in a row that England's top women's player Boulter and de Minaur have played on rival teams in the United Cup.
In Perth, Tsitsipas suffered defeat to a plucky Shevchenko after making 40 unforced errors to 17 in an hour and 52 minutes.
Alexander Shevchenko accounted for Greek star Stefanos Tsitsipas in Perth. (Richard Wainwright/AAP PHOTOS)
Greece were consigned to more misery, with Maria Sakkari losing 6-4 6-3 to Elena Ryabkina in the women's singles.
In the first of the two Monday night sessions, embattled world No.2 Iga Swiatek brushed off her doping controversy to lead Poland to a 2-1 win over Norway in Sydney. Â
Swiatek trounced Malene Helgo 6-1 6-0 before teaming with Jan Zielinski to edge out Casper Ruud and Ulrikke Eikeri 6-3 0-6 10-8 in a match tiebreaker in the deciding mixed doubles rubber.Â
Ruud had levelled the tie with a 7-5 6-3 win over Hubert Hurkacz in the men's match but Norway's defeat ended the Scandinavians' quarter-final hopes after they also lost their opening tie against Czechia.
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