PERTH (AFP) -- Novak Djokovic suffered a frustrating fitness saga as a wrist problem led to the Serb's upset 6-4, 6-4 loss to Australia's Alex de Minaur in the quarterfinals of the United Cup in Perth on Wednesday, Jan. 3.

Djokovic, who received multiple massages on court on his troublesome right wrist -- hurt in training 24 hours earlier -- fell victim to an inspired de Minaur, who led his side into the weekend semifinals in Sydney.

Ajla Tomljanovic then sealed the 2-0 win for the team with her 6-1, 6-1 defeat of Serb 184th-ranked substitute Natalija Stevanovic.

Stevanovic had replaced an exhausted Olga Danilovic, who featured in previous ties here alongside Djokovic.

World number one Djokovic produced 31 unforced errors as his 43-match win streak in Australia was ended after 93 minutes on court against de Minaur.

"I was not on my level, it was just one of these days where you didn't feel your best," Djokovic said.

"Your opponent played very well. That's all I can say.

"I think I have enough time to get myself in the right shape for the Australian Open, and that's what matters the most at this point.

"I knew I was not going to be at 100 per cent physically, emotionally, mentally game-wise in the opening week of a season.

"It's all a part of the build-up for the Australian Open, that's where I want to perform at my best."

Victory marked revenge for the low-key de Minaur, beaten by Djokovic a year ago at the Australian Open.

The 24-year-old Australian was recording his first victory over a world number one, adding Djokovic to a list which also includes Rafael Nadal, the number two whom he beat here a year ago.

"This was extremely special, Novak is an unbelievable competitor," de Minaur said.

"This feels surreal, I'm happy to do it here in Australia. When you go against Novak you just have to try and enjoy it.

"You must keep fighting to the end. Today was my day -- I'm happy I was able to get the win.

"This one means a lot."

Djokovic was seen twice by the trainer in the opening set and at one point said: "The more I'm playing, it's getting worse."

The 36-year-old with 10 Australian Open trophies was broken once per set, his second mis-cue coming on a double-fault.

Poland power past China

Earlier, top-ranked Poland overpowered China, with Hubert Hurkacz and Iga Swiatek propelling them into the semifinals with a singles sweep.

The pair of straight-set victories in Perth put the tie out of reach and sent the Poles into a clash against either Norway or France in Sydney.

Adrian Mannarino and Caroline Garcia had earlier booked France a last eight tie against the Norwegians with victory over Italy.

Hurkacz secured a clinical 6-3, 6-4 defeat of Zhang Zhizhen before world number one Swiatek followed up, winning nine games on the trot at one point to beat Zheng Qinwen 6-2, 6-3 despite losing serve twice.

Swiatek was eager to get to Sydney as the first nation to qualify for the semifinals of the 18-nation mixed team tournament.

"Bondi Beach here we come," she said, after swatting aside Zheng who was the 2023 WTA Most Improved Player. "I'm looking forward to a day off."

Hurkacz fired 10 aces as he dismissed Chinese number one Zhang.

"It's always a tough match with him. He can play some amazing shots," the winner said.

In Sydney, journeyman Mannarino, who enjoyed his best-ever season last year, swept past Lorenzo Sonego 6-4, 6-4 before Garcia overcame a stubborn Jasmine Paolini 6-4, 5-7, 6-4.

It gave France an unassailable 2-0 lead to put them into the knockout rounds.

The last quarterfinal slot will be decided when Greece meet Canada, with the winner facing the best runner-up from group play in Sydney.

The Sydney quarterfinals are played on Thursday and Friday before the semis on Saturday and the final a day later.