One has to wonder what was going through Roger Federer’s mind when Kei Nishikori completed his improbable upset of top-ranked Novak Djokovic on a blistering hot Saturday afternoon at the US Open.

Roger’s biggest obstacle to an impossible 18th major title seemed to have just been removed from his path. Federer had never lost against his semifinal opponent Marin Cilic in five tries (the last victory came just a few weeks ago in Toronto), and while Nishikori has beaten Roger twice before, Monday’s title match would be Nishikori’s first ever appearance in such a bout. Few would favor a Slam final debutant against a living legend of the game.

However, the hypothetical Federer-Nishikori final vanished in a storm of haymakers that lasted all of one hour and 45 minutes and produced a most unlikely scoreline:

Marin Cilic def. Roger Federer 6-3, 6-4, 6-4

The 25 year-old Croatian put together what he described later as the best performance of his career. Here are a couple of numbers to illustrate his point:

– Of the 91 total points won by Marin Cilic, 43 came via outright winners. That’s good for 47%, or as it’s more commonly called, almost half.

– The 14th seed lost only 6 points played on his first serve (out of 45).

What made Marin’s performance so impressive was that Federer didn’t exactly shame himself out there:

– Roger served 61% of 1st serves, including 12 aces (only 1 fewer than Cilic). That’s a pretty decent serving performance.

– Federer committed just 17 unforced errors. 3 in the first set, 9 in the second, and just 5 in the third.

So how exactly did Marin Cilic, a man who can’t even say he’s won an ATP 500-level event, pull this off?

With power. With incredibly clean hitting, particularly on the backhand side. With a simple, yet very effective gameplan. Cilic looked to push Federer behind the baseline, particularly on the backhand side, creating lots of open space on Roger’s Deuce court. The Croat produced some sensational serve returns, limiting Federer to just 48% of points won on his second delivery. Marin even came up with some blistering passing shots, particularly off the backhand wing.

It was brilliant big-man tennis, with equal parts thumping pace and equal parts coherent tactics.

The match got out of hand for Federer pretty quickly. Cilic produced a simply remarkable return game at 1-2 in the first set. Roger was up 40-0 in that service game, but seemed helpless as Marin placed thumping return after thumping return within inches of the baseline. There wasn’t any time for Federer to react. Cilic won five straight points and took a somewhat surprising lead.

Roger had a chance in the very next game to get back on serve, but the break point was snuffed away by a couple of Cilic overheads. That break point would end up being half of all break chances created by Federer during the match.

If there is one aspect of the 17-time major champs’ game that didn’t make an imprint in the match, it was the return game. Federer won only 27% of all return points, a number that is incredibly low given the fact that Cilic served only 51% of 1st serves. Usually a tennis player would love the sight of so many second deliveries. Not Roger today, who only managed to win 44% of those points. The Swiss needed to do more with those chances, given how dominant the Cilic first serve had been.

It must be said, though, that Cilic employed a simple and brilliant gameplan with his second serve. Unlike Gael Monfils two days ago, Cilic focused on hitting good kick serves to Federer’s backhand on almost every single second serve point. Roger struggled to take those returns on the rise and rarely got any depth on them when the returns managed to go over the net. Thus, Cilic was able to start points played on his second serve with great court positioning, something he rarely failed to waste.

The second set got off to an even faster start than the opener: Cilic went up 0-40 on the very first game of the set. Federer saved two of the break points, but couldn’t fend off a third as Cilic thumped yet another great return near his feet. Roger wouldn’t threaten Cilic’s serve for the rest of the set, failing to create a single break point chance.

The third set started in a more positive way for Federer, though. After holding serve to start, Federer finally created a chance to break in the next game. Not only that, but the Swiss sealed the break almost immediately, sending the pro-Federer crowd into a frenzy. At this point, the atmosphere on Arthur Ashe stadium resembled a fevered Davis Cup tie: any outcome favorable to the 5-time former champ was greeted with a thunderous roar.

Given the many travails of Marin Cilic’s career when trying to produce an upset (or hold onto a lead), many thought they were in for a repeat performance of Federer’s comeback from down two sets to Monfils.

But Marin Cilic had other ideas.

Instead of retreating into his shell after getting broken for the first time in the match, the Croat came out guns blazing in the very next game, getting a 15-40 lead in what seemed like no time. Moments later, Cilic managed to kill two birds with one stone: he broke Federer to get back on serve and also managed to silence the previously delirious crowd.

The match returned to the tone set by Cilic through two sets: the 25 year old standing firm on the baseline pushing the 33 year old further and further back. His timing was impeccable, his aim true. It didn’t seem like a shock when Cilic created chances to break at 3-all. As the second chance was taken, another little trend continued: while Federer saved half of the break points he faced throughout the match, he never really escaped any of the games in which Marin Cilic created a chance to break. So while the Croat went 4 for 8 on break points, he went 4 for 4 on breaking serve in games in which he created at least one break chance.

The men traded a couple of holds, and soon Marin Cilic lined up to try and serve out the match. The man who has never made a Masters 1000 final had a chance to book his ticket for his first Grand Slam final. Many feared the worst, given Cilic’s history of collapses. But this is how Marin Cilic handled this 5-4 service game – perhaps the most important service game of his life:

Ace. Ace. Ace. Backhand down the line winner.

And that was that.

Marin Cilic gifted us a simply sublime performance, and by doing so, made it possible for tennis fans to see a Major final without any of the Big 4 of Federer, Nadal, Djokovic, and Murray. The last time this happened? When Marat Safin and Lleyton Hewitt squared off in the 2005 Australian Open final.

While it’s tempting to mourn the end of what has been an unparalleled era of dominance by the 4 shining knights of the ATP, it’s more appropriate to resist said temptation, and instead celebrate a uniquely gorgeous performance.

Take a bow, Marin Cilic. You more than deserve it.