Djokovic leads Serbia into United Cup quarters

Novak Djokovic led Serbia into the quarter-finals of the United Cup on Tuesday despite struggling with a sore right wrist which required on-court treatment.

The world number one dropped a set in grinding past the Czech Republic's Jiri Lehecka 6-1, 6-7 (3/7), 6-1 and required several visits from the trainer.

He did not take part in the deciding mixed doubles, instead watching from the team bench as Olga Danilovic and Hamad Medjedovic defeated Czech pair Miriam Kolodziejova and Petr Nouza 4-6, 7-6 (7/2), 10-8.

It put Serbia into a last-eight clash with Australia on Wednesday.

The result means that defending champions the United States are out, with one more day of play in Perth to go before the event shifts to its weekend finish in Sydney.

"I managed to play through the wrist problem," 24-time Grand Slam champion Djokovic said of his wrist issue, which comes barely a week ahead of the Australian Open.

"It's not the first nor the last time," he said. "These things happen. I have to manage it and find a solution.

"I finished the match, now we'll see what happens."

Czech Wimbledon winner Marketa Vondrousova started the tie by defeating Danilovic 6-1, 3-6, 6-3, handing Djokovic a comeback assignment as he took on Lehecka to take it to the deciding doubles.

"It was amazing, I didn't have luck in singles but thank god we have Novak with us," Danilovic said after sending Serbia through.

"Hamad and I came back, we fought so hard. I"m happy to get the win and go into the quarter-finals."

The 113th-ranked Medjedovic added: "I know how tired Olga was, she gave everything she could, and did it for us."

Poland will face China in the other Perth quarter-final on Wednesday.

Greece crush Chile 2-1

In Sydney, Australian Open contender Stefanos Tsitsipas also struggled with an injury, to the lower back.

The Greek world number six was expected to meet Chilean number one Nicolas Jarry, but sat it out, leaving teammate Stefanos Sakellaridis to step up.

Sakellaridis, just 19 years old and ranked 416, put up an outstanding fight against the 19th-ranked Jarry, but fell short 6-3, 3-6, 7-5.

"It was an incredible match, very tough for me," said Jarry. "Stefanos played amazing. I think he was grinding a lot, so it was a very tough opponent and I'm happy to be able to be there mentally."

Greek world number eight Maria Sakkari had earlier earned a commanding 6-0, 6-1 victory over Chile's outclassed Daniela Seguel.

Sakkari, the highest-ranked Greek woman in history, took just 68 minutes to crush Seguel, who was facing a top-20 player for the first time in her career.

She did not face a break point until the last game of the match, and successfully erased the chance

Tsitsipas returned for the crucial mixed doubles decider with Sakkari, but they lost 6-7 (5/7), 6-3, 10-6 to Seguel and Marcelo Tomas Barrios Vera.

"It's amazing, amazing," Barrios Vera said. "It's our second match as a team, so we're super happy."

Tsitsipas, who reached the Australian Open final last year, losing to Djokovic, was clearly struggling on serve late in the match, grimacing as he held his back.

While watching Sakkari's singles, he told the host broadcaster "there are a few chances I might not play and there are a few chances that I might" against Chile.

"I'm kinda 50-50 so far. We'll wait and see."

A six-time Grand slam semi-finalist, Tsitsipas has 10 ATP Tour titles to his name, but is still searching for a first major win.

Donna Vekic and Borna Coric helped win Croatia against The Netherlands 2-1