Kei Nishikori US Open
Kei Nishikori celebrates after his incredible win over Novak Djokovic in the semifinals of the US OpenReuters

Japan's Kei Nishikori and Croatia's Marin Cilic rocked the tennis world with stunning back-to-back US Open semifinal upsets on Saturday, sending two all-time greats Roger Federer and Novak Djokovic out of Flushing Meadows.

On an extraordinary day that will go down as one of the most surprising in Grand Slam history, 10th seeded Nishikori denied Djokovic a fifth straight trip to the US Open final when he toppled the world number one 6-4, 1-6, 7-6 (4), 6-3 on a sweltering Arthur Ashe Stadium court.

Then, before a disbelieving crowd had fully absorbed what they had just witnessed, 14th seeded Cilic sent a new round of tremors across the US National Tennis Center by sweeping past 17-time Grand Slam champion Federer in snappy one hour, 45 minutes.

When the dust had settled the year's last Grand Slam was left with a final no one would have predicted between Cilic, who missed last year's tournament sitting out a doping ban and Nishikori, the first Asian man to ever reach a Major final.

Adding to the magnitude of Saturday's events, Monday's final will be the first Grand Slam title decider without either Rafael Nadal, Federer or Djokovic since the 2005 Australian Open when Marat Safin defeated Lleyton Hewitt.

"I think it's exciting for the game to have different faces from time-to-time," said Federer when asked about his thoughts on a Nishikori-Cilic final. "At the same time, I think people still enjoy seeing the guys they have seen for a while or often in the big matches.

"But I think it's definitely refreshing to some extent. It's big for Croatia and big for Japan I guess on some level, especially on sporting terms and tennis terms.

"Everybody who gets to this stage of this kind of a competition deserves to be there because they have put in the work and they hoped for the break and this is it for both of them. I hope they can play a good final."

Certainly it will not be the marquee final fans and television executives had hoped for.

Between them, Federer and Djokovic have won 24 grand slam titles, including six US Opens. Nishikori and Cilic have won none and had never before been beyond the semifinals of a Grand Slam.

Despite the lack of a big name, the final should be an entertaining one between the big-hitting Cilic and the no-quit counter-punching Nishikori.

"It's going to be special day for both of us," said Cilic. "Opportunity for both of us to win a Grand Slam, to be a part of the history. It's going to be definitely huge emotions on the court.

"We have different game styles. I think I'm going to have to just focus on my game...and to try to serve well. I think it's going to be a good sort of tactical matchup for the final."

Certainly no one worked harder or longer for their place in the final than Nishikori.

In a remarkable display of endurance, the 24-year-old Japanese followed up punishing five-set wins over third seed Stanislas Wawrinka and fifth seed Milos Raonic with an even more extraordinary effort, grinding down Djokovic in two hours, 52 minutes on a sweltering Arthur Ashe Stadium court.

Nishikori arrived on Saturday looking fresh despite having played the latest finishing match ever at the US Open on Tuesday in the fourth round against Raonic, when he walked off court at 2:26 am local time.

Two days later, the Japanese was forced to go the distance again, outlasting Wawrinka in a four hour, 15 minute battle.

In total a tireless Nishikori logged 11 hours 16 minutes of court time in his last three matches.

In contrast, the powerful 6-foot-6 Cilic wasted little time in blasting past Federer to record a first win over the Swiss master at his sixth attempt.

Federer had no answer to his opponents' booming service game and heavy groundstrokes as Cilic completed the win with three aces and a sizzling backhand winner up the line as he served a love-game to close out a startling afternoon of tennis.

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