Frances Tiafoe has delivered a winning encore to Jessica Pegula's spectacular upset of world No.1 Iga Swiatek to give the USA a 2-0 lead over Poland in the opening United Cup semi-final in Sydney.
Pegula reversed a run of four straight losses to Swiatek with a commanding 6-2 6-2 victory over the reigning French and US Open champion and hot Australian Open favourite.
Tiafoe, a 2022 US Open semi-finalist, then lived up to expectations with a 6-3 6-3 win over world No.245 Kacper Zuk in the opening men's singles match to ram home Team USA's advantage ahead of Saturday's remaining three rubbers.
Poland will need to win all of those matches to snatch the tie, starting with world No.10 Hubert Hurkacz's tussle with the ninth-ranked Taylor Fritz.
Magda Linette faces 2022 Australian Open semi-finalist Madison Keys in the second women's singles encounter before Swiatek and Hurkacz are scheduled to take on Pegula and Fritz in the potentially decisive mixed doubles.
Pegula will be brimming with confidence if she is called upon for another live rubber on Saturday.
Hardly a slouch herself after rising to No.3 in the rankings following a stellar 2022 campaign, the inspired 28-year-old never blinked under a closed roof at Ken Rosewall Arena.
Pegula broke Swiatek five times and dropped her own serve only once in storming to her first win over the three-time grand slam champion since 2019.
"I've played her in a lot of different places but I definitely feel like these were the fastest conditions," Pegula said.
"Also Poland had a tough turnaround yesterday (flying from Brisbane) and we've been lucky enough to have been playing here, and maybe have a little bit of an advantage in being used to the courts.
"So I wanted to take that and use it as much as I could and I did a really good job playing really aggressive, serving smart and returning really well."
Unbeaten in nine singles and doubles matches between them, Pegula (5-0) and Tiafoe (4-0) have put the USA in the box seat to be the first team through to Sunday's final.
"Let's just keep going. Let's win this thing," Tiafoe said.
"My confidence has been pretty high for a little bit. I've been playing some of the best tennis of my life right now and I'm just having fun out there on court.
"Just competing, comfortable in myself, comfortable in my game, and I'm happy with where I'm at - but I can get better."
In the evening semi-final, Italy took a 2-0 lead over Greece.
World No.27 Martina Trevisan stunned the fancied Maria Sakkari 6-3 6-7 (7-5) 7-5.
Trevisan showed more composure when it mattered against the error-prone Greek world No.6 before Lorenzo Musetti dominated Stefanos Sakellaridis as expected 6-1 6-1.
Matteo Berrettini can seal a spot in the final for Italy with a first-up win over Stefanos Tsitsipas on Saturday.
Italy has further fallbacks with Lucia Bronzetti favoured to beat Despina Papamichail in the other women's singles before the final mixed doubles.