And so it has proved. The "Big Three'" have been in brilliant form thus far, with flashes of the dominance that has seen them win all but two of the Wimbledon singles titles since 2003 (Andy Murray has won those other two).
Roberto Bautista Agut, the No. 23 seed from Spain, is the "other" person making up this year's final four, and he will face defending champion Djokovic in one of Friday's semifinals, with Nadal and Federer meeting in the other for their first Wimbledon clash since the epic final of 2008.
So how will things play out? We turned to ESPN's writers at Wimbledon to get their thoughts.
Is the dominance of the Big Three at Grand Slams more about their excellence or lack of competitors who can break through?
Pete Bodo: Entirely about their excellence. There hasn't been any kind of mysterious ailment or virus that affects all but the Big Three. Any number of players and/or circumstances could have derailed one of these icons or significantly altered the narrative while they were accumulating their 53 Grand Slam singles titles. But it didn't happen. As Djokovic said after his quarterfinal victory: "Nadal, Federer and myself, in a way we go onto next level in terms of tennis and focus. We're very dedicated to these tournaments." We might be watching the three greatest players of this or any other era.
Alyssa Roenigk: A bit of both. As we are seeing on the women's side right now, excellence is one thing. Sustained excellence is another. Having each other as great rivals has elevated all of their games to a level that is tough to crack at this point, particularly late into Slams. So far, no giant killer has been able to back up a B3 takedown by winning a Slam. But they're coming. (We see you, Stefanos Tsitsipas.)
D'Arcy Maine: To some extent, it's both, but I think it's more due to their collective excellence. They are really just that good when it counts and in the big moments. When it's best of five, as it obviously is in the Grand Slams, it's just that much harder for an upset to happen, and these three have the experience, knowledge and the talent to pull out the win, even against tough, young opponents.
Tom Hamilton: It's their unrelenting excellence but equally their mental fortitude. Every year we talk about whether they are coming to the end of their reign -- pretenders have tried but failed to dent that force field. The trio's showing in 2019 has laughed in the face of the doubters.
Simon Cambers: It's more about their excellence. These three guys are going to go down in history as the three best players of all time and it is their consistency, across the board, that has kept the next generation in its place. And their dominance has created auras that others have not been able to cope with.
What is your favorite moment from the Rafa-Fed rivalry?
Bodo: I still love that moment when they made the joint decision to pull out of the 2006 Hamburg tournament (then a prestigious Masters 1000 event) on the Monday the event started. The reason? The two warriors were spent after going to the wire in the Sunday final in Rome -- Nadal won it, 6-7(0) 7-6(5) 6-4 2-6 7-6(5) -- less than 24 hours earlier. The Rome Masters match was just their sixth meeting. The Rafa = clay/Fed = grass narrative hadn't struck roots yet, and it was an exciting preview of what these two men would accomplish over the years.
Roenigk: Easily the 2008 Wimbledon final. There are few tennis matches I, a casual fan at the time, can remember well enough to tell you where I was and what I was doing when they took place. (Watching from a friend's house in Park City, Utah, over July 4 weekend.) This March, Nadal withdrew before his scheduled semifinal match with Federer at Indian Wells, so I've never seen them play each other in person. I might change my answer after Friday night.
Maine: There are so many amazing moments, it should be hard to choose -- but the 2008 Wimbledon final has literally been called "the greatest match ever" by so many over the years, and it's hard to argue. Federer had won the previous five singles titles at the All England Club, and Nadal was looking for his first one, and there was just this palpable feeling, and so much tension throughout. You could see how much they both wanted it. It went on for what felt like forever, and was just one of those epic battle of wills that should live on forever in sports lore. Hard to top that.
Hamilton: It's always hard to park the memories of that remarkable 2008 Wimbledon final, but once you mix that with the previous year's final, then in those two matches you have the perfect grasp of this rivalry. In 2007, Nadal faced Federer in the Wimbledon final but was left in tears after failing to see off his nemesis on grass. A year later, after the final to end all finals, it was Nadal standing triumphant. Over the space of a year, memories of his heartbreak in 2007 stayed with him, and it spurred him through in one of the greatest sporting moments of the 21st century.
Cambers: At Wimbledon, it has to be their 2008 final. An obvious choice, maybe, but that final had everything, the perfect contrast in styles, perhaps when the two men were close to their very best level. That Nadal could come out on top, on Federer's best surface, was a monumental achievement.
What will be the key to Friday's Rafa-Fed match?
Bodo: With these two, it will come down to which of them handles the big points and pressure situations better. Sure, Rafa will have the advantage in the rally game, and Fed is the superior attacker. But Nadal has a better net game than he gets credit for, and Federer's groundstrokes, particularly the forehand, have been devastating. Remember, though, that Nadal has always specialized in breaking down those groundstrokes, especially the Federer one-handed backhand. The grass will give Federer better looks than he gets on clay against Nadal, but the rally game -- Nadal's specialty -- rules these days at Wimbledon.
Roenigk: Nadal has the confidence of a recent win over Federer at the French and a chip on his shoulder (see my prediction below), both of which will serve him well Friday night. Although it's hard to bet against Federer on grass, I'm going to. Nadal has looked in top form this tournament, having dropped only one set, to Nick Kyrgios in the second round, and the only thing better than Nadal's service games has been his returns.
Maine: Nadal won their most recent meeting handily at the French Open just a few weeks ago, so momentum is very much on his side, but, this is Federer on grass, so he has the edge there. Federer said the 2017 Australian Open final (which he won in five) might be the most relevant match with Nadal to work off of heading into this semi, and what won it for him that day might be the key to victory for either player -- aggressively attacking, dominating with a powerful serve, winning the long rally points, and just staying as consistent as possible. It's cliché to say this, but with players of this caliber, and who are so familiar with one another's game, it really will probably come down to who wants it more and who can just get his level slightly higher than the other one.
Hamilton: Federer has had his wake-up call, having lost the first set against Kei Nishikori in the quarterfinal, while Rafa Nadal is storming along nicely, thanks to his straight-sets win over Sam Querrey. Nadal is the master at gamesmanship, pushing the 25-second serve rule to its maximum, and has also conquered the art of challenging calls. Aggression is key here: If it's a baseline battle then Nadal wins, and Federer will have to match fire with fire. Nadal is playing some beautiful, tactical tennis -- as he showed against Querrey -- and if he has opportunities to play those neat drop shots near the net and moves Federer around then it'll be the Spaniard in the driving seat. For Federer, he needs to mix the pace up, get in the way of Nadal's game and time management and cause some unease.
Cambers: The Federer serve. He's been concerned here this year about how difficult it's been to hit aces or unreturnable serves, and he'll need plenty of them if he's to hit through Nadal, who's been playing great. If Federer serves close to his best, he'll win.
What would Bautista Agut have to do to beat Djokovic?
Bodo: Bautista Agut will need to have a career serving day if he hopes to keep Djokovic at bay. Djokovic is on fire. He's been nearly flawless since surviving that tougher-than-it-looked third-round battle with rising talent Hubert Hurkacz. But don't expect this to be a walk in the park for Djokovic. RBA is the least well known of this generation's excellent grass-court performers. He has a clean, relatively flat game, and fine movement. His main problem is that nobody moves better than Djokovic. Bautista Agut's forehand is his superior ground shot, so look for Djokovic to work on his backhand.
Roenigk: Well, he's done it before -- the past two times they've met, actually, at Doha in January and Miami in March. But both of those victories came on hard courts. The two have actually never faced each other on grass, a much more unpredictable surface. Those wins, however, will serve Bautista Agut as well as any tactic, by giving him the belief that he can beat the world No. 1.
Maine: Pray? Eat a balanced breakfast? If I knew I would probably be a coach at this point, but he is going to need to play a nearly flawless match, and hope it's an off day for Djokovic, and then he might have a chance. However, the way the world No. 1 has been rolling through this tournament makes that seem incredibly difficult.
Hamilton: Play the game of his life. This is his first Grand Slam semifinal and while his wonderfully unpredictable forehand is a potent weapon, he'll need to bring his A-game if he is to knock Djokovic off his stride. He will need to be far more aggressive, improve on his serve returns and generally be a huge nuisance if he is to cause a major upset.
Cambers: Play out of his mind. Djokovic is a little better at every part of the game than Bautista Agut, much as he was in the matchup with David Goffin, which means he should win in straight sets. I just don't see an upset.
What are your predictions for both semifinals?
Bodo: Djokovic will end Bautista Agut's excellent run at Wimbledon, because he shares most of the Spanish challenger's best qualities but none of his weaknesses -- one of which is Bautista Agut's inexperience playing for such enormous stakes. Djokovic's ground game has been nothing less than relentless at this tournament. As Goffin said after Djokovic won their quarterfinal, "It's just incredible. He's (Djokovic) just crushing everything in his way." Nadal has survived a very tough draw that included three players whose games are big enough to take the racket out of any opponent's hand. That has boosted his confidence and provided good preparation for facing Federer's excellent serve. It's hard to see Federer sustaining a sufficiently high level of attacking tennis to keep Nadal from returning to the final for the first time since 2011.
Roenigk: Rafa is on a roll, and he's likely still seething over Wimbledon seeding him behind Fed. I say he rolls right into the final. He'll meet Djokovic there.
Maine: Djokovic wins easily in straight sets (sorry, Bautista Agut, but enjoy your bachelor party!), and Federer and Nadal have another epic battle with Federer advancing to the final after five grueling sets.
Hamilton: Djokovic will win in straight sets while Nadal will see off Federer in four to tee up what promises to be the most memorable of finals.
Cambers: Djokovic in straight sets; Nadal in four.