For Nadal it will be his 38th Grand Slam semifinal appearance.
The other men's semifinal will be No. 1 Novak Djokovic against No. 9 Cam Norrie.
The women's semifinals tonight NZT will be 2019 champion Simona Halep against No. 17 Elena Rybakina, and No. 3 Ons Jabeur against unseeded Tatjana Maria.
Halep advanced by eliminating No. 20 Amanda Anisimova of the United States 6-2, 6-4, and Rybakina came back to defeat Ajla Tomljanovic 4-6, 6-2, 6-3.
Nadal leads Kyrgios 6-3 in their head-to-head series, but they are even at 1-all at Wimbledon: Kyrgios, just 19 and ranked 144th, announced himself to the world by stunning Nadal in 2014; Nadal won the rematch in 2019.
Give Kyrgios credit for honesty: Even he did not think this day ever would arrive. Kyrgios became the first unseeded and lowest-ranked man to get to the final four at the All England Club since 2008 by playing what, for him, amounts to a restrained and efficient brand of tennis.
"I thought my ship had sailed," Kyrgios said. "Obviously, I didn't go about things great early in my career and may have wasted that little window. But just really proud of the way I've just come back out here."
Kyrgios, who is ranked 40th, has garnered more attention for his behaviour on and off the court than his skills with a racket in hand. His match against the unseeded Garin, a 26-year-old from Chile, came a day after police in Canberra, Australia, said that Kyrgios is due in court next month to face an allegation of common assault stemming from something that happened in December.
"I have a lot of thoughts, a lot of things I want to say, kind of my side about it," Kyrgios said at his post-match news conference Wednesday. "Obviously I've been advised by my lawyers that I'm unable to say anything at this time."
After his first-round victory at Wimbledon last week, Kyrgios was fined $10,000 for spitting in the direction of a heckling spectator. His third-round victory over No. 4 seed Stefanos Tsitsipas was as contentious as can be, and Kyrgios was fined another $4,000 for an audible obscenity; afterward, Tsitsipas called him a "bully" and "evil."
Worth noting, too, is how well Kyrgios has been playing. His serve, in particular, is among the best in the game, regularly topping 130 mph, and he pounded 17 aces against Garin while getting broken just once — in the very first game, at love.
His big forehands are terrific, too, but little else is conventional about Kyrgios. One example: "I don't have a coach," Kyrgios said with a smile. "I would never put that burden on someone."