Coco Gauff rode to the rescue with a 6-1, 6-1 hammering of Solana Sierra to nudge the United States towards a 2-1 defeat of Argentina on Saturday at the United Cup.
The defending champions trailed 0-1 after Sebastian Baez had earlier shocked sixth-ranked Taylor Fritz 4-6, 7-5, 6-4, despite the American firing down 23 aces.
"I'm so happy, I'm pleased to give a point to Argentina. I felt very confident today," Baez said.
Fritz suffered a minor ankle roll late in the match which put him off his power-hitting game and he was unable to close the gap on Baez, who beat the 28-year-old for the first time in six meetings.
Gauff and Christian Harrison eventually clinched the tie in the mixed doubles decider, defeating Maria Lourdes Carle and Guido Andreozzi 6-4, 6-1.
"I'm really happy, there was a bit of pressure," Gauff said. "I know I can play even better, I want to continue this."
Stan Wawrinka launched the final season of his career with a marathon 5-7, 7-6 (7/5), 7-6 (7/5) win over Arthur Rinderknech to give Switzerland an unassailable 2-0 lead over France.
The 40-year-old joined teammate Belinda Bencic as a winner after she began the tie 6-2, 6-4 over Leolia Jeanjean. The Swiss won the mixed doubles for a 3-0 final scoreline.
Wawrinka is competing in Perth for the first time, needing to battle for nearly three-and-a-half hours to defeat an opponent a decade his junior.
The three-time Grand Slam champion sealed victory on his first match point and said: "It's amazing to have such support on my first time here.
"After 20 years on the tour it's amazing to finally play here. Today's match was tough but I'm happy we could start 2-0."
Also Saturday, in Sydney, Zhang Zhizhen led China to a 2-1 win over Belgium to begin their tournament.
Norway's Casper Ruud stunned Australian No 1 Alex de Minaur 6-3, 6-3, while Aussie women's singles substitute Storm Hunter beat Malene Helgo 6-2, 7-6 (7/3) when illness stopped first choice Maya Joint.
Hunter and John-Patrick Smith won the doubles over Ulrikke Eikeri and Viktor Durasovic 4-6, 6-1, 10-4 for Australia's 2-1 final scoreline.
The United Cup has 18 nations and is a mixed-team event spread across Perth and Sydney that serves as build-up to the Australian Open later this month.