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

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 Serbian 184th-ranked substitute Natalija Stevanovic.

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

World No. 1 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 percent 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 No. 1, adding Djokovic to a list which also includes Rafael Nadal, the No. 2 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."