Il Nuovo Postiglione - Injury retirements hit China Open but Sinner reaches semis unscathed

Zheng's first tournament since Wimbledon was cut short in the third set against the Czech Republic's Linda Noskova, who reached the last 16 having been 3-0 up in the decider.

China's Olympic champion Zheng said afterwards her return from recent elbow surgery had come too soon.

"Okay, now I know to compete third set, the amount of hitting the balls is too much for me," she said.

Poland's Iga Swiatek, the top seed, advanced having won the first set 6-0 when Camila Osorio of Colombia called it quits.

"I'm sorry for Camila because she's always giving her 100 percent," six-time Grand Slam champion Swiatek said.

"It's always pretty sad to see that because we want to just compete. She wasn't able to."

The 24-year-old Swiatek had no such injury trouble but said she might skip tournaments in future to protect her health.

The amount of matches in the tennis calendar has been a major talking point in recent years, with players such as Novak Djokovic cutting back the number of tournaments they compete in as they near the end of their careers.

- 'Pretty crazy' -

Starting last year, the Women's Tennis Association made it mandatory for top players to participate in all four Grand Slams, 10 WTA 1000 events -- which includes Beijing -- and six 500-level tournaments.

Swiatek called the requirements "pretty crazy", adding that "people are more fatigued" especially in the second half of the season.

"I think we have to be smart about it, not really unfortunately care about the rules and just think what's healthy for us," she said.

Underlining the point, Swiatek next plays Emma Navarro after the American's opponent Lois Boisson of France was unable to finish their last-32 encounter.

In one match that was completed, American Jessica Pegula beat Britain's Emma Raducanu 3-6, 7-6 (11/9), 6-0 and will next face Ukraine's Marta Kostyuk.

Injury also struck in the men's quarter-finals as Jakub Mensik and Lorenzo Musetti both retired from their matches.

Italy's Sinner meanwhile beat the world no. 57 Hungarian Fabian Marozsan 6-1, 7-5 in one hour and 19 minutes and next plays third seed Alex de Minaur.

"Generally I'm very happy with today's performance," said Sinner, the world number two, who boasts a 10-0 record against the Australian De Minaur.

Sinner won the first set with ease but Marozsan made it more difficult in the second, breaking for a 5-4 lead.

That spurred Sinner into action, winning the next three games with just one dropped point to power into the last four.

Teenager Learner Tien of the United States moved into the semi-finals when Italy's Musetti retired due to leg pain in the deciding third set.

Tien faces either eighth seed Daniil Medvedev of Russia or second-seeded German Alexander Zverev.

E.Scozzafava--INP