San Francisco Frontiers - Injury worries for Djokovic, Tsitsipas as Serbia squeeze into quarters

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 quarter-final play in Perth to go before the event shifts to a weekend finish in Sydney.

"It happened in the warm-up today before the match," said Djokovic of the wrist issue, which comes barely a week ahead of his defence of the Australian Open.

"I basically got constant treatment before the match, during the match, after the match, you know, trying to address the issue that I'm facing today in the best possible way.

"I know professional sport in general, these things happen. I think it's not a major concern, because I still managed to finish the match and managed to play well, even though I maybe wasn't feeling 100 percent.

"Hopefully I'll have enough time to recover for tomorrow's tie against Australia," added the 24-time Grand Slam champion.

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 in the doubles.

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.

- Lower back pain -

In Sydney, Stefanos Tsitsipas, beaten by Djokovic in the Australian Open final last year, 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.

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

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.

In the other Sydney tie, Donna Vekic and Borna Coric overcame Arantxa Rus and Tallon Griekspoor respectively to give Croatia an unassailable 2-0 lead over the Netherlands.

D.Parker--SFF