Boulter showed no sign of off-season rust as she cruised to an easy 6-2 6-3 triumph in 86 minutes at Sydney's Ken Rosewall Arena.
Billy Harris, replacing an injured Jack Draper, can clinch victory for Great Britain if he beats Tomas Etcheverry in the men's singles later on Monday before the mixed doubles match.
Katie Boulter in action in her win over Nadia Podoroska. (Mick Tsikas/AAP PHOTOS)
Ranked world No.24, Boulter seemed to enjoy a home crowd advantage at the Sydney hard court as fiance Alex de Minaur watched in the stands.
Her win helps give Australia a fighting chance in the group stages after they lost 2-1 to Argentina on Saturday.
"He's definitely out here supporting because he needs us to win today," Boulter said of de Minaur.
"To keep Australia's hopes alive, they need a two-one win and I'm obviously out here trying my hardest.
"I'm very lucky to have that support."
Boulter is commanding the court with her forehand right now 💪— United Cup (@UnitedCupTennis) #UnitedCup | @katiecboulter pic.twitter.com/NWWvBp98oADecember 30, 2024
Boulter announced her engagement to the Australian No.1 on Christmas eve after almost four years of publicly dating.
Great Britain and Australia are set to play each other on New Year's Day, but Boulter is unlikely to come face-to-face against de Minaur in the mixed doubles with Matt Ebden and Ellen Perez on 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.
Boulter is set to return to the court on Monday with Charles Broom against Podoroska and Etcheverry.
Poland play Norway in the later match in Sydney, with Iga Swiatek taking on Malene Helgo.
At Perth's RAC Arena, Greece play Kazakhstani with Stefanos Tsitsipas first off against Alexander Shevchenko.
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