Kei Nishikori and Marin Cilic rewrite the script on a wild Saturday at the U.S. Open

It's tough to know how to feel about the upside-down, landscape-altering day of tennis we witnessed Saturday. Kei Nishikori outlasted Novak Djokovic. Marin Cilic obliterated Roger Federer. Nishikori and Cilic are about to play each other for the U.S. Open title. I'm still trying to wrap my head around it. 

Surprising things like this happen in sports all the time. But men's tennis is different. Being a fan of men's tennis this past decade means being conditioned to expect the expected. This wasn't part of the plan. 

As a fan watching these big tournaments, I always feel a certain tension between the various outcomes I want to see. Fun as the upsets are to root for, and thrilling as they are to witness, sometimes the predictable result - the one in which the two ostensible top players track their collision course, win all the matches they're supposed to, and have their date with destiny in the final - is the one that really appeals to me. 

While that outcome can make the six rounds leading up to the final seem like a formality, years of indelible championship matches - between the likes of Federer and Rafael Nadal, Nadal and Djokovic, Djokovic and Andy Murray - have not only produced gorgeous tennis, but added chapters to increasingly interesting and complicated rivalries.  

At the same time, the prospect of having our expectations upended is a pretty crucial part of the sport-watching endeavor. For better or worse, women's tennis hasn't had the same constancy as the men's game. A day like today would've been just another Grand Slam semifinal. A surprising one, to be sure, but nothing earth-shaking. (Dominika Cibulkova had been past the third round exactly twice in 23 Grand Slams before she marched to the Australian Open final this year.) 

For the past several years, women's tournaments have been compelling because of the number of people who can realistically win them. Men's tournaments have been compelling because of the few men who do win them; because of the clarity with which they separate themselves from their peers. 

You'll hear some people argue that this constancy is what makes men's tennis special. The sport is blessed with a handful of transcendent talents, and having those transcendent talents continually stacked up against each other in the finals of the biggest tournaments can only be a good thing. When Nadal pulled out of the tournament, Djokovic and Federer became the overwhelming consensus favorites to meet in the final. And after their epic five-setter at Wimbledon this year, few were going to complain if they played for the trophy again. 

For a while, they were both breezing through their draws. Then suddenly, in the quarters against Gael Monfils, Federer looked vulnerable. He went down two sets and then faced two match points. He came about as close as you can come to losing without actually doing so. 

With his stunning comeback fresh in mind, I sort of expected Djokovic to pull off something similar Saturday, even as he wasn't playing close to his best and Nishikori had him on the ropes. The magnetic pull of preordination was supposed to carry him through. 

It didn't, of course. And by the time Federer found himself down two sets to Cilic, I no longer sensed any cosmic force hovering around him, ready to grab him under the armpits and lift him up if need be. I sensed, instead, that it was time for him to fall. 

Cilic and Nishikori both played magnificently Saturday, and both are wholly deserving of their places in the final. When they play Monday, it will be the first time since the Australian Open in 2005, a run of 38 majors, in which the final doesn't feature one of  Djokovic, Federer, or Nadal. I don't know if it will be a good match. I don't know what outcome I'll root for. I don't know a lot of things. This is unfamiliar territory.  

What I do know is that Saturday signaled a broad tectonic shift within the sport. We've been talking about men's tennis moving towards an era of greater parity for some time, but it's never really felt real until now. Before this tournament, Federer, Nadal, and Djokovic had still accounted for five of the six Grand Slam finals appearances this year. The VIP room largely remained closed to outsiders. 

But with Cilic coming out of nowhere and playing by far the best tennis of his career, and with Nishikori cashing in on the promise he showed in the Spring (before being derailed by a back injury and falling off everyone's radar), it feels like it's finally time to recalibrate our notions of who can get in the door. Stan Wawrinka cracked it open in Melbourne. Nishikori and Cilic just busted it down.