PERTH, Australia (AP) — Coco Gauff and Taylor Fritz powered the U.S., tournament winner two years ago, into the semifinals of the United Cup mixed teams tennis event on Wednesday, Jan. 1.

In the first singles match, Gauff had a 7-6 (4), 6-2 win over China's Zhang Shuai. Fritz then made sure of victory for the U.S. by edging Zhang Zhizhen, 6-4, 6-4.

“Shuai was playing amazing tennis out there. I was literally on the ground for most of the match,” world No. 3 Gauff said. “The harder I hit, the harder she was hitting. I felt like I couldn’t get her on defense.”

The No. 4-ranked Fritz said he didn't want to let Gauff down.

“There was a little bit of pressure because I didn’t want to be the one who loses it for the team after Coco won all her matches this week,” he said.

The Americans completed a 3-0 sweep when Desirae Krawczyk and Robert Galloway beat Zhang and Sun Fajing 6-3, 6-7 (1), 10-3 in the mixed doubles. The U.S. next meets either Italy or Czech Republic, who play their quarterfinal on Friday.

Kazakhstan also advanced to the semifinals with a 2-1 win over a Germany team playing without the injured world No. 2 Alexander Zverev.

Zverev was a late scratch due to a biceps injury. He was scheduled to face Alexander Shevchenko but withdrew at the last minute with Kazakhstan leading the tie 1-0 after Elena Rybakina beat Laura Siegemund 6-3, 6-1.

Shevchenko beat Zverev's replacement, Daniel Masur, 6-7 (5), 6-2, 6-2 to clinch the tie while Zverev watched from the sidelines. Germany won the later mixed doubles.

Shevchenko took a medical timeout due to heat exhaustion while leading 1-0 in the second set. He came back from the break to dominate the rest of the match.

“It was a heat problem for sure,” Shevchenko said. “I had a bit of a headache, my head was spinning. It was a struggle this match. To play in this heat was so tough."

Kazakhstan next meets Poland or Britain, who play Thursday in Sydney, where all remaining matches in the tournament will be played.

In Sydney, Iga Swiatek and Hubert Hurkacz won their deciding mixed doubles match over the Czech Republic to qualify Poland for the quarterfinals.

World No. 2 Swiatek and Hurkacz beat Tomáš Macháč and Karolína Muchová 7-6 (3), 6-3 in the decider at Ken Rosewall Arena. The Polish team led 5-2 before allowing the Czechs back into the first set.

In earlier singles, Macháč gave the Czech Republic the lead with a 7-5, 3-6, 6-4 win over Hurkacz before Swiatek evened the tie with a 6-3, 6-4 win over Muchová.

Also in Sydney, Katie Boulter's 6-2, 6-1 win over Olivia Gadecki of Australia helped Britain clinch a quarterfinal place.

Boulter went into the match in the knowledge that a straight-set victory would ensure Britain's progress to the last eight as Group F winner.

“I've been trying to avoid all the stats ... but we were at dinner with (former British No. 1 Laura Robson) last night and she thankfully told me I had to win in straight sets,” Boulter said.

Alex de Minaur, who is engaged to marry Boulter, drew the host level with a 6-2, 6-1 triumph over Billy Harris before he combined with Gadecki to defeat Charles Broom and Olivia Nicholls 6-3, 7-6 (3) in the mixed doubles. Australia's 2-1 victory, though, was not enough to qualify the team for the last eight.