Gauff defeated Maria Sakkari 6-3, 6-2, giving the defending champion United States a 1-0 lead over Greece, News.Az reports, citing ESPN.
Taylor Fritz will have the chance to follow up in singles against Stefanos Tsitsipas, with the winner advancing the Americans to the semifinals in Sydney on Saturday.
Earlier in the week, Gauff posted on social media just before her singles match, aiming to clarify her recent remarks about American tennis fans.
The ensuing match didn't go well for the No. 4-ranked Gauff, who lost the first five games and struggled in a 6-1, 6-7 (3), 6-0 loss to No. 42 Jessica Bouzas Maneiro. But Fritz won his singles match and Gauff and Christian Harrison combined in mixed doubles to clinch top spot in Group A and advance the Americans to the quarterfinals.
"I think I was striking the ball well today, and when that happens, my movement on the court is also good," Gauff said Wednesday. "I usually know it's going to be a good day."
In a night quarterfinal at Perth, Stan Wawrinka, playing in his farewell tour this year before retiring, was scheduled to lead Switzerland against Argentina.
At Sydney, Hubert Hurkacz and Iga Swiatek were victorious in their singles matches to give Poland a winning 2-0 lead over Netherlands and a place in the quarterfinals from Group F.
