PHOTO: AFP
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.
Nadal, 31, the 16-time Grand Slam champion, revved up a gear to surge through the tie break in the second set, although there was concern at one point during the second 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."
Also into the semi-finals is the Australian Nick Kyrgios, who was up 6-0 and 3-0 when Belgian qualifier Steve Darcis retired.
Kyrgios faces the number two seed Alexander Zverev of Germany or Russia's Andrey Rublev.
Simona Halep took a step nearer overhauling Garbine Muguruza as world number one when 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.
The pair met at the French Open earlier this year, with Ostapenko winning the duel.
The Spaniard Muguruza's short stay at the top is under severe threat after she bowed out in the first round in the Chinese capital with a virus.
Halep is in red-hot form and closing in.
She claimed the scalp of former number one Maria Sharapova in the previous round -- beating the Russian at the eighth attempt.
Petra Kvitova became the third woman into the semi-finals when she defeated fellow Czech Barbora Strycova.
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