Poland took revenge on holders the USA to set up a United Cup final against Switzerland in Sydney despite Iga Swiatek suffering defeat to Coco Gauff on Saturday.
The Swiss beat Belgium by the same 2-1 scoreline in the other semi-final, with Belinda Bencic playing a starring role.
Hubert Hurkacz beat Taylor Fritz 7-6 (7/1), 7-6 (7/2) to put Poland, beaten by the United States in last year’s final, ahead in the tie.
World number four Gauff struck back for the Americans with a dominant 6-4, 6-2 win over Swiatek.
It was Gauff’s fourth consecutive victory over the world number two and a statement win with the Australian Open just over a week away.
Gauff reappeared soon after to team up with Christian Harrison in the deciding mixed-doubles match, only to go down 7-6 (7-5), 7-6 (7/3) to Katarzyna Kawa and Jan Zielinski and put Poland in the final.
In the other last-four clash, Stan Wawrinka lost in three sets in gruelling heat of more than 40C but Switzerland beat Belgium.
The Tokyo Olympic champion Bencic had put Switzerland in front with a battling 6-3, 4-6, 7-6 (7/0) victory over Elise Mertens in two hours and 37 minutes.
“It feels like 170 kilos fell off my shoulders -- I was so stressed, I really wanted to do well and today I felt so much pressure to not let my team down,” Bencic said.
Then it was over to the 40-year-old Wawrinka, a three-time Grand Slam champion who was on Friday handed a wildcard to the Australian Open starting on January 18.
Wawrinka, playing his final year before retirement, fought back to force a deciding set against Zizou Bergs, but the Belgian ultimately won 6-3, 6-7 (4/7), 6-3 in two-and-a-half hours.
That meant the semi-final went down to the mixed doubles, with Bencic and Jakub Paul defeating Bergs and Mertens in another tight battle.
“The team spirit is amazing and it starts with the captain,” Bencic said, referring to Wawrinka.
“He’s supporting all throughout my match and then he goes out to play his own match and then he’s back to support the doubles.
“It starts with him but then with all the energy from our bench it gives us such a spirit to win.”
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