The 31-year-old Spaniard prevailed 6-4, 7-6 at the Olympic Green Tennis Center in Beijing, despite earlier being troubled with his vision.

"Just something came to my eye, that's all," Nadal, who is aiming to win the men’s competition for a sixth time, said.

"I think it was just a hair or something, a hair from the tennis ball. 

"It was bothering me for a while.

"It was not important, but I am still feeling it a little bit."

Awaiting Nadal in the penultimate round is third seed Grigor Dimitrov of Bulgaria after his 7-6, 4-6, 6-2 victory over Spain's Roberto Bautista Agut.

Australia's Nick Kyrgios will face Germany's Alexander Zverev in the other semi-final.

Krygios was leading Belgium’s Steve Darcis 6-0, 3-0 when his opponent retired injured. 

Second seed Zverev, meanwhile, beat Russia's Andrey Rublev 6-2, 6-3.

In the women’s event, world number two Simona Halep of Romania is through to the semi-finals with a 6-2, 6-1 win over unseeded Russian Daria Kasatkina.

Victor edges Halep closer to taking the world number one ranking held by Spain’s Garbiñe Muguruza, who bowed out of the tournament in the first round with a virus.

She will now have an opportunity to avenge her French Open final loss to Jelena Ostapenko after the Latvian defeated Romania's Sorana Cirstea 6-4, 6-4.

Petra Kvitová is also through to the semi-finals after overcoming fellow Czech Barbora Strýcová 6-3, 6-4.

She will meet unseeded Frenchwoman Caroline Garcia, who beat Ukrainian third seed Elina Svitolina 6-7, 7-5, 7-6.