Sinner defies doping case to reach Beijing last four

Top-ranked Jannik Sinner on Monday defied the controversy surrounding his doping case to join Carlos Alcaraz and Daniil Medvedev in the Beijing 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) on Saturday said 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 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.

Alcaraz and Medvedev, the second and third seeds respectively, meet in the other semi-final.