Rafael Nadal was leading world number four Tomas Berdych 4-2 in the first set of their semi-final match of the ongoing China Open when the Czech was forced to retire with a back problem.
This means the 27-year-old Spaniard will return to the number spot of the ATP rankings on Monday, having reached the final of the Beijing Open.
It will mark his return to the top of the rankings since July 2011 after winning the french Open and the US Open this year.
Nadal, who returned to action in February after eight months hiatus, has won ten titles in 2013. He has not lost a match since losing to Belgian 135th seed Steve Darcis in the first round of Wimbledon in June.
In the second semi-final coming up on Saturday, Rodger Federer takes on France’s fifth seed Richard Gasquet.
Meanwhile, in the women’s tournament, Serena Williams powered through her match with Caroline Wozniacki 6-1 6-4.
The Danish sixth seed only briefly offered resistance, breaking Williams’s serve in the sixth game of the second set before forcing the world number one to go on the offensive in a 38-shot rally in the seventh.
But Williams extinguished any hope of a comeback by maintaining her two-game lead up until the conclusion of the set.
In her semi-final game, the top seed will play either Angelique Kerber or Agnieszka Radwanska, who play Friday evening.
It was heartbreak for Chinese star Li Na, who was dumped out in her quarter-final match 4-6 6-2 6-4 by Petra Kvitova.
The 2011 French Open winner has twice reached the semi-finals in Beijing, and looked set for her third appearance, but the 31-year-old still awaits her first major title on home soil.
Kvitova will face Jelena Jankovic in the semi-finals. The Serb defeated Czech Lucie Safarova after an early scare, eventually dumping out her opponent 6-7 6-4 6-4.