Federer was the first of the two to book his spot into the final four, dropping serve in the first game of the match and eventually dropping the first set to Kei Nishikori, before bouncing back to win comfortably after two hours and 36 minutes, 4-6, 6-1, 6-4, 6-4.
It was an historic win for Federer, his 100th career match win at Wimbledon, making him the first man in to record 100 career match wins at a single Grand Slam.
Nadal followed the Swiss into the semifinals with a 7-5, 6-2, 6-2 win over Sam Querrey, hitting 43 winners to just 12 unforced errors to win in two hours and six minutes on No. 1 Court. The Spaniard sealed the victory with one last forehand winner—his 21st of the match.
Nadal and Federer will now square off for the 40th time, with Nadal leading the overall head-to-head, 24-15. It will be their 14th meeting at a Grand Slam tournament, with Nadal leading that head-to-head, 10-3. It will be their fourth meeting on grass, with Federer leading, 2-1.
The Swiss won their first two meetings on grass in the 2006 Wimbledon final, 6-0, 7-6 (5), 6-7 (2), 6-3, and in the 2007 Wimbledon final, 7-6 (7), 4-6, 7-6 (3), 2-6, 6-2. But the Spaniard won their last one in the 2008 Wimbledon final, 6-4, 6-4, 6-7 (5), 6-7 (8), 9-7.
The two rivals also just competed against each other in the French Open semifinals, with Nadal prevailing, 6-3, 6-4, 6-2.
"Well, we have a lot of information on Rafa, and so does he about us," Federer said after his win on Wednesday. "You can either dive into tactics for two days or you can just say it's grass-court tennis, and I'm going to come out and play attacking tennis, and if he can beat me, then that's too good.
"We had some brutal conditions when we played at Roland Garros this year, but it was a joy to play against him there, on his court. I'll just go about this one like every other match."
"It's really difficult to imagine being in this situation again, but here we are," Nadal said after his win over Querrey. "I'm just excited about the victory of today right now, but of course I'm excited to play against Roger again at Wimbledon after such a long time."
In his post-match press conference, Federer pointed to a specific part of Nadal's game that has improved over the years that might make him even more dangerous on grass.
"He's improved so much over the years on this surface," the No. 2-seeded Swiss said. "He's playing very differently than he used to. We haven't played each other in a long, long time on this surface. He's serving way different—I remember back in the day how he used to serve, and now how much bigger he's serving, how much faster he finishes points.
"It's impressive to see how healthy he's stayed. A lot of them were saying, 'Oh, it's the end, by 2008.' Similar to me in '09. We're still here. It's nice to play each other again."
Nadal was asked about his improved serve, as well.
"I am running less, so I need to serve better," he said. "I probably cannot play 20 weeks per year anymore, so I need to reschedule my planning to improve things to be very competitive every single time that I am on court.
"Of course I'm serving better. Of course I'm hitting the backhand better. Maybe volleying better, slicing better—but even like this, I don't know if my level today will beat my level of years ago.
"In terms of re-adapting our game, talking about me and Roger, for sure there are a lot things we find to improve to keep being one of the best in the world."
And will his win over Federer at Roland Garros five weeks ago help him at Wimbledon?
"It's difficult to say yes or no—it's probably better to have that victory than have defeat, of course, but in the other hand, it's a completely different situation," Nadal said.
"Playing on grass and clay, it's probably the biggest change in the world of tennis."