Rafael Nadal got some tennis ball fibre lodged in his eye but that did not stop the world number one setting up a China Open semi-final on Saturday with "great guy" Grigor Dimitrov.

The Spaniard tamed the big-serving American John Isner 6-4, 7-6 (7/0) on Friday to set up the clash with the third-seeded Bulgarian.

Dimitrov booked his place in the last four on Beijing's outside hard courts with a 7-6 (7/5), 4-6, 6-2 victory over another Spaniard, Roberto Bautista Agut.

The other semi-final will be an intriguing encounter between two rising talents, with temperamental but talented Nick Kyrgios playing starlet Alexander Zverev of Germany.

Nadal, 31, the 16-time Grand Slam champion, revved up a gear against Isner to surge through the second-set tie break, although there was concern at one point during the set when he appeared to be suffering an eye problem.

"Just something came to my eye, that's all," said Nadal, who is chasing a sixth title this year.

"I think it was just a hair or something, a hair from the tennis ball. It was bothering me for a while."

"Not important, (but) I am still feeling (it) a little bit by the way," Nadal, who attempted to wash the suspected fibre out with water, added with a smile.

Nadal will face a familiar figure in Dimitrov -- the pair practised together at Nadal's base in Mallorca before the US Open, where the Spaniard won the title for a third time this year.

They even went fishing together, but Nadal said they will have their game faces on for Saturday:

"At the end of the day we are competitors.

"We go on court and we try our best and we want to win.

"Of course, he is a player that I really have like a good friend on the tour. He's a great guy."

Kyrgios, 22, enjoyed an easy passage into the last four when Belgian qualifier Steve Darcis retired at 6-0 and 3-0 down.

The 20-year-old Zverev, like Nadal also searching for a sixth title in a breakthrough season, had few scares in dispatching Russia's Andrey Rublev 6-2, 6-3.

The comfortable victory propelled Zverev into the ATP Finals in London for the first time, joining Nadal and Roger Federer for the end-of-season spectacular.

- Halep eyes top spot -

Simona Halep is on the cusp of overhauling Garbine Muguruza as world number one after the Romanian raced into the semi-finals of the women's draw.

The second-ranked Halep eased past Russia's unseeded Daria Kasatkina 6-2, 6-1 in 69 minutes and will face Latvia's Jelena Ostapenko.

Halep, 26, will usurp Muguruza at the top if she reaches the final in Beijing.

Halep and Ostapenko met in the final at the French Open earlier this year, with the Latvian winning the duel.

But Halep is in red-hot form and claimed the scalp of former number one Maria Sharapova earlier this week, beating the Russian at the eighth attempt.

Petra Kvitova, the two-time Wimbledon champion from the Czech Republic, faces in-form Caroline Garcia of France in the other semi-final.

Garcia outlasted world number three Elina Svitolina of Ukraine in three gruelling late-night sets, 6-7 (5/7), 7-5, 7-6 (8/6), in a match lasting nearly three-and-a-half hours and finishing close to 1:00 am.

Source: AFP