Top-ranked Jannik Sinner defied the controversy surrounding his doping case to join Carlos Alcaraz and Daniil Medvedev on Monday in the China Open semi-finals.

The defending champion will face either Andrey Rublev or Chinese wildcard Bu Yunchaokete after defeating Jiri Lehecka 6-2, 7-6 (8/6) for his 14th win in a row.

The 23-year-old is under the microscope after the World Anti-Doping Agency (WADA) said on Saturday it was seeking a ban of up to two years after he twice tested positive for traces of the steroid clostebol in March.

The International Tennis Integrity Agency (ITIA) cleared the Italian of wrongdoing in August and allowed him to continue playing, and weeks later he won the US Open for his second major title.

The ITIA accepted Sinner’s explanation that the drug entered his system when his physiotherapist used a spray containing it to treat a cut, then provided massage and sports therapy to the player.

WADA has appealed the case to the Court of Arbitration for Sport (CAS).

On the tennis court, the world number one recovered from a set down to win his first two matches in Beijing but he made a fast start against the 37th-ranked Lehecka from the Czech Republic.

Sinner surged through the first set of their quarter-final but there was little between them in the second as they traded some thunderous groundstrokes.

They went to a tie break, where Sinner saved two set points on the way to victory.

Four-time Grand Slam champion Alcaraz plays last year’s runner-up Medvedev after emerging from a tense first set to defeat Russian seventh seed Karen Khachanov 7-5, 6-2.

Russian third seed Medvedev beat unseeded Italian Flavio Cobolli 6-2, 6-4.

Alcaraz and 2021 US Open champion Medvedev have met seven times before with the Spaniard winning five of their meetings, most recently in the semi-finals at Wimbledon.

“When he’s in the zone he’s probably the best player in the world,” Medvedev said of the second seed.

“I feel like now he’s in the zone, so it’s a great test for me.”

In the women’s draw, Naomi Osaka set up a last-16 clash with Coco Gauff while top seed Aryna Sabalenka and Olympic champion Zheng Qinwen both sailed through.

Four-time major champion Osaka defeated American Katie Volynets 6-3, 6-2 and faces American fourth seed Gauff in a showdown of former US Open title-holders.

“It’s definitely going to be a battle — who wants to take control of the point first,” said Osaka, a former number one now ranked 73.

“And I think it’s going to be me.”

Osaka is playing her first tournament under Patrick Mouratoglou, the Frenchman best known for being the long-time former coach of Serena Williams.

The 26-year-old Japanese won four majors from 2018 to 2021 — the US Open and Australian Open, both twice.

She is also a former winner in Beijing and has said she feels at home on the hard courts of the Chinese capital.

But Osaka has struggled for consistency since returning to tennis in January after the birth of her daughter Shai. Her best results after becoming a parent have been two quarter-final appearances.

World number two Sabalenka will take some stopping after the US Open champion swatted aside Ashlyn Krueger 6-2, 6-2 for her 14th victory in a row. She plays another American next in Madison Keys.

Zheng, the home hero playing in China for the first time since winning gold in Paris, rolled over Nadia Podoroska of Argentina 6-3, 6-2.

Jasmine Paolini became the biggest casualty so far when the third seed was beaten 6-4, 6-0 by 31st-seeded Magda Linette.