Iga Swiatek, the favorite for this month's Australian Open, was in tears after losing at the United Cup on Friday.
The US and French Open champion sobbed courtside after being thrashed 6-2, 6-2 by American Jessica Pegula in the mixed-team tournament semifinals in Sydney.
"I was just sad. But it is not the first time I cried after a lost match, nothing special," world No.1 Swiatek said.
The victory by Pegula helped the U.S. seize a 2-0 lead against Poland, while Italy also claimed both opening matches against Greece.
The remaining singles will be played Saturday, with a mixed doubles to be held if required.
Pumping her fist throughout a thrilling clash with world No. 6 Maria Sakkari, Italy's Martina Trevisan won 6-3, 6-7 (4), 7-5 in a match lasting 3 hours, 14 minutes.
The No. 27-ranked left-hander danced with glee inside Ken Rosewall Arena after the triumph before hugging teammates.
"Oh my God, it was a great battle today, and I am really, really, really happy. It was amazing," Trevisan said. "Sometimes I had to smile because it helped me to relax and remember that I am here in this amazing stadium with a lot of people, so life is beautiful.
"I am so happy with this because I continue to work every day to keep improving and to feel better on the court, and I think I deserved it today."
Teammate Lorenzo Musetti scored a 6-1, 6-1 victory over Greece's Stefanos Sakellaridis.
As compelling as Trevisan's encounter with Sakkari proved, it was the manner of Swiatek's defeat and her distress that was the talking point.
Swiatek won all four clashes against Pegula last year and is hoping to do well at the Australian Open beginning Jan. 16. But the assertive play of Pegula, who adopted an aggressive position when returning serve, reaped rich rewards for the world No. 3.
After a lengthy toilet break at the end of the first set, Swiatek was able to edge ahead for the first time when holding her opening service game to start the second set. But Pegula held her concentration and form to break away for a convincing victory.
Swiatek downplayed her emotional reaction and dismissed suggestions that travel issues from Brisbane to Sydney on Thursday had an impact on her performance.
"I kind of felt hopeless today because mentally and physically I wasn't able to kind of show up, even, and problem solve," Swiatek said. "So it is always hard when you lose, especially when you're kind of playing for the team and your country."
Pegula, who reached the quarterfinals in three Grand Slam tournaments last year, said she benefited from her familiarity with Ken Rosewall Arena and the swiftness of the court. The American was based in Sydney during the group stages of the inaugural tournament, while Poland and Italy played in Brisbane and Greece featured in Perth.
"I wanted to take that as much as I could and use it as much as I could, and I thought I did a really good job of playing aggressively, serving smart and returning really well," Pegula said.
Frances Tiafoe later gave the U.S. a 2-0 lead over Poland by defeating Kacper Zuk 6-3, 6-3.
Taylor Fritz can clinch a spot in the final for the U.S. when he plays world No. 10 Hubert Hurkacz in the third singles. Matteo Berrettini has a similar opportunity for Italy when he faces Greek star Stefanos Tsitsipas.