Harriet Dart of the Britain defeated Maddison Inglis in straight sets to secure the team’s tie win over Australia at the United Cup.
With victories on day one for Cameron Norrie and Katie Swan, Britain led their group opponents 2-0.
After Ajla Tomljanovic withdrew with a knee injury, Inglis was a late call-up for the match.
Britain won with two matches to spare after Dart won 6-4, 6-4 on Friday.
Dan Evans was defeated 6-3, 7-6 (7-3) by Jason Kubler, and Dart and Jonny O’Mara were defeated 7-6 (7-4), 6-4 by Sam Stosur and John Peers in a doubles match.
The United Kingdom will now prepare to face their other group opponents, Spain, with the first match taking place on Saturday between Norrie and Rafael Nadal.
On the same day, Swan will face Nuria Parrizas-Diaz.
Six round-robin groups of three teams will compete in the inaugural mixed-team tournament.
The Britain, Spain, and Australia are vying for a chance to face the United States, Germany, or the Czech Republic in a play-off to advance to the semi-finals.