NEW YORK -- When the smoke cleared after the final Grand Slam event of the year, the landscape in men's tennis was bathed in a clear, pleasant light and the details stood out clearly.

Novak Djokovic dominates the game at the moment, so much so that speculations have started about his chances to match or surpass Roger Federer's record haul of 17 Grand Slam singles titles.

Wait -- didn't we just go through something like this a little while ago with some other guy?

Yes, but ... Djokovic's victory over Federer on Sunday at the US Open capped a summer that demands a rethinking of how we rank the greatest rivalries of the Open era. It also might have significantly altered that lively GOAT (Greatest of All Time) conversation, as well. Djokovic joined Federer and Rod Laver as one of the only three men in the Open era to reach all four Grand Slam finals in the same year. Sunday's win also gave the world No. 1 three Grand Slam titles for 2015.

"He's perfected his game on hard court, no doubt about it," Federer said after losing the four-set final when asked how many majors Djokovic might salt away. It was a significant concession, given that two of the four majors are contested on hard courts, and Djokovic already has set an Open-era record with his dazzling success at the Australian Open.

"[Djokovic] always was a great clay-court player," Federer continued, "and because he moves as well as he does, he's solid and consistent now on grass. To say the least, it's very impressive. He's having an unbelievable career."

Djokovic and Federer are also having an unbelievable rivalry that is already challenging Djokovic's wars with Rafael Nadal in volume and in quality. Sunday was the 42nd meeting between the US Open finalists, and it left them deadlocked with 21 wins apiece. Nadal has played Djokovic two more times, both wins for Nadal.

Both rivalries easily overshadow the next best in tennis: Ivan Lendl's 21-15 edge on John McEnroe and even Pete Sampras' 20-14 career advantage against Andre Agassi.

Nadal-Djokovic clashes tended to be four- or five-hour knockdown, drag-out demonstrations of trench warfare waged from distant baseline outposts. They have been wars of attrition featuring superb masters of defensive tennis.

With his US Open win on Sunday, Novak Djokovic now has 10 career Grand Slam titles on his résumé. TIMOTHY A. CLARY/AFP/Getty Images

By contrast, Djokovic versus Federer has the same kind of pleasing contrast presented by Lendl vs. McEnroe or Sampras vs. Agassi -- the attacker versus the defender and counterpuncher; glitzy offense (in Federer's case, that super-flashy SABR offense) crashing against a wall of gritty defense.

The three most recent matches between Djokovic and Federer (the finals at Wimbledon, Cincinnati and the Open, all within roughly a month) invited fickle tennis fans to wonder what they ever saw in those grueling Djokovic-Nadal matches in the first place. And if they didn't, the recent struggles from Nadal, who finished this year without a Grand Slam title for the first time in a decade, might have accomplished the same thing.

No one is silly enough to mistake news reports for gospel truth, but the way players interact with the media often give us more insight into their state of mind than the words they utter, or withhold. Nadal, who was humble, honest and patient with the media throughout his highly publicized travails this year, finally cracked at this tournament after grappling with his slump.

"I am No. 8 in the world; I am not No. 100," Nadal said in his news conference after his second-round victory against Diego Schwartzman. "I am not so bad. After I arrive here with the victory, I come back to the locker room [hearing outsiders] saying how bad I am. Every day. ... [It] seems like I come here and if I am saying the truth, if I am being honest, it is bad. ... I don't know what you want of me."

The incident opened a small window into the frustration Nadal has bottled up inside. It also suggested that the former No. 1 and holder of 14 Grand Slam titles has plenty of issues to sort out before he's ready to take a run at reasserting his claim as Djokovic's greatest rival. That leaves Federer time to make hay while the sun is shining.

Rafael Nadal was ousted in the third round of the US Open with a five-set loss against Fabio Fognini. Elsa/Getty Images

This shift in the order of tennis merit probably began in earnest at the start of 2014, when Stan Wawrinka crashed the Big Four party and upset Nadal in the Australian Open final (ominously, Nadal nursed a bad back in that match, although Wawrinka certainly played a high-quality match).

That now seems ages ago, but it's barely been a year and a half. At the time, Nadal was hot on Federer's trail of Grand Slam records, having added two majors in 2013 (along with five Masters 1000 titles). With 13 Grand Slam titles to Nadal's name (and presumably at least a few more to come), and a clear head-to-head advantage against Federer (23-10), many people believed it was just a matter of time before he would lay claim to the Greatest of All Time title.

But Nadal stalled in that Melbourne final and has since won only one major (2014 French Open) and a single Masters event. Nadal's claim to superiority is melting away as he squirms and struggles, while Federer still makes it look easy, astonishing fans, and rivals, at the age of 34.

It's hard to tell how much longer Federer can go on, or how many more times he might lock horns with Djokovic. But they might already have created the best rivalry in tennis; it's certainly the most interesting in terms of the contrast in styles.

Federer resolutely marches on in the history books, and he's still hearing footsteps behind him. This time they belong to a different guy. At least for now.