Federer beat Kei Nishikori 4-6 6-1 6-4 6-4 to become the first man to achieve a century of victories at the same grand slam on Thursday (AEST).
The 20-time major champion had forgotten that he had made history until he was reminded by a spectator after his latest imperious performance on Centre Court.
Eight-time Wimbledon champion Federer said: "It's special. I guess so. It's been a lot of years I've been coming here. That's given me the opportunity to win a lot naturally.
"I didn't think of it while I was playing today. Actually not at all, not once. Then as I'm signing, the guy says, 'Congratulations for your 100'. Oh, yeah, I didn't know. I forgot."
"It's nice, because if I look back at the hundred that have happened, some were so incredibly cool. Today again was a big match going into the semis, facing Rafa. Yeah, a hundred wins here at Wimbledon. Who would have thought? I didn't, for sure."
Nadal defeated Sam Querrey to set up another blockbuster showdown with his old rival 11 years after they last met at the All England Club, when the Spaniard won a classic final.
Federer said of Nadal: "He's improved so much over the years on this surface. He's playing also very different 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 sort of healthy he's stayed. A lot of them are saying, 'Oh, it's the end,' by 2008. Similar to me in '09. We're still here. So it's nice to play each other again."