KEY BISCAYNE, Fla. -- They were whistling with genuine anger Thursday afternoon when Roger Federer won his way into the Sony Ericsson Open semifinals.
No, not at the 16-time Grand Slam singles champion, but at his opponent, Gilles Simon, who retired from the match -- after losing the first three games -- complaining of a stiff neck. Those who felt they were cheated of more than a glimpse of the stylish Swiss player let loose.
"He got booed off the court -- that's rough," an amused Federer noted in an on-court interview. "He couldn't move. Hey, it happens to all of us."
The macro view, of course, was quite different.
Around the world, tennis fans were congratulating themselves on their good fortune. Now, only Rafael Nadal's Thursday night quarterfinal match against Tomas Berdych stood in the way of the next chapter in the greatest tennis rivalry of our generation, maybe ever.
"I would love to play Rafa, clearly," Federer had said earlier. "I think it would be electric out there tomorrow night."
About five hours later, Nadal did his part, albeit in a very different fashion, squeezing by Berdych 6-2, 3-6, 6-3.
And so, on Friday night, before a packed house, Rafa and Roger will go at it for the 23rd time. It feels a little weird that they're playing in the semifinals, but that's on Federer for falling to the No. 3 ranking. Still, it's happened three times before, most recently at the Tennis Masters Cup in 2007.
What's really special about this one is the venue. Nadal-Federer has played on stages all around the world: four times in Paris, three at Wimbledon and Monte Carlo, as well as places like Rome, Dubai and Hamburg. But -- quiz time, tennis fans -- when was the last time they brought their act to the United States?
Crack open a frosty ginger ale for yourself if you said Miami 2005. That's right, it's been six years since we've seen them jousting on American soil. Interestingly, their first two encounters ever were here in Miami. As a 17-year-old in 2004, Nadal surprised Federer in straight sets of a third-round match. A year later, the Spaniard won the first two sets in a best-of-five final, but Federer survived a third-set tiebreaker and won the last two sets 6-3, 6-1.
And now, after 20 meetings outside of the U.S. box, we have a prime-time matchup in Eastern Standard Time.
"My No. 1 rival to me it seems is Rafa," Federer said. "Doesn't matter how many more times I'm going to be playing all the other guys. At the moment, we have that history and nobody can take it away from us. Clearly, those are the matches I'm really looking forward to and hoping to play my best tennis.
"If you win, great; if you lose, that's OK, too, as long as you tried everything and learned something else from that match after you lost. But I am planning to win, and that's why I have to be well prepared. It would obviously be nice to play here in the States."
Federer was thrilled he had to play only three games against Simon and, after winning his three previous matches in straight sets, should be quite fresh. Asked if he'd watch the Nadal-Berdych match on television, Federer was coy.
"It depends how dinner goes," he said, smiling.
"One match away," Federer said later in his postmatch news conference. "Let him do the work. I'll be sitting on the couch.
"No, that's not nice."
While Nadal tore it up last year, winning three of the four Grand Slams, he seems to have cooled off a bit this season. In fact, you can argue that after the 24-0 Novak Djokovic, Federer has been the second-best player. He's 21-3 -- and all of those losses were to Djokovic.
In his fourth-round match against Olivier Rochus, Federer was phenomenal against the player he has known since the age of 13. Rain backed things up and the two started play at 12:37. Only 52 minutes later, it was over. Federer won 6-3, 6-1, with a plus-20 ratio of winners to unforced errors.
Nadal had been efficient, winning all of his previous sets, against Kei Nishikori, Feliciano Lopez and Alexandr Dolgopolov. He's 17-3 for the season, losses coming to Djokovic in the Indian Wells final, as well as Nikolay Davydenko (Doha) and David Ferrer (Australian Open).
The ongoing rivalry between Rafa and Roger soon may be skewed by the success of Djokovic. After diligent research, far beyond the call of duty, the ATP World Tour determined that this is the 18th time the big three have landed in the same semifinals. For the record, Nadal has won the most titles in those events (six), but five of them came on clay. Federer has five and Djokovic four.
"In the beginning I guess I struggled to embrace the rivalry I had with Rafa," Federer said. "Only later on I was able to say this is actually quite cool. Sleeveless, pirate pants, you name it, long hair, lefty, spins, more with the flat shots and so forth and double-handed against one-handed, lefty against righty.
"I think it all kind of made sense, and I was able to embrace it then.
"I think we had some good times in the past, and they have changed into what it is today. Really respectful and helping each other for good causes, foundation matches, you name it, for tsunamis. We've done so many things together.
"It's been a lot of fun."
Greg Garber is a senior writer for ESPN.com.