US Open 2014: Marin Cilic at 'the peak of the world' after victory over Kei Nishikori

The Croatian won his first Grand Slam last night

Marin Cilic (GETTY IMAGES)

Marin Cilic struggled to comprehend his sudden elevation to become tennis' newest grand slam champion.

The 25-year-old arrived in New York as a player who had never challenged for any of the sport's biggest prizes, but leaves as US Open champion.

Cilic overwhelmed his fellow surprise finalist Kei Nishikori 6-3 6-3 6-3, carrying the momentum from his stunning semi-final victory over Roger Federer and turning it into major silverware and a cheque for three million US dollars.

The Croatian said: "It seems completely unreal to be called a grand slam champion. I was dreaming about this all my life and suddenly the last four or five days everything started to change.

"And with my tennis especially. I started to play absolutely unbelievable, starting with the fifth set with (Gilles) Simon. After that I had an unbelievable run of matches against these top guys.

"It means everything. It's just a huge accomplishment and a huge moment for myself and for my team and for everybody around me who was with me all these years supporting me, believing in me and never giving up. So this is just the peak of the world."

A year ago Cilic was not even in New York, instead serving a provisional suspension ahead of a doping ban, which was initially nine months but reduced to four on appeal.

The time away from the tour allowed him to work on his game and also gave him a tougher edge that was on display at Flushing Meadows.

The other significant change was Cilic's appointment of long-time mentor Goran Ivanisevic as his coach, with the former Wimbledon champion finally persuading his charge to use his natural attacking gifts.

Cilic is the first Croatian slam champion since Ivanisevic and he revealed the pair have been sticking to certain rituals, including not shaving - although watching Teletubbies has not been on the agenda this time.

"He's brought to the team a very relaxed atmosphere, besides extremely huge knowledge," said Cilic.

"The help he brought to me, I feel that the fun is the best spice of everything, that I think collects all the other pieces together. Every day with him is extremely fun."

Goran famously joked there were three of him during his Wimbledon run, but Cilic added: "With personalities, I think he has only one and that's with a very big heart."

It was tough to believe the stadium would not have been fuller had the final been between Novak Djokovic and Federer rather than the men that beat them, even at 5pm on a Monday.

After all the talk of the end of the big four, this was the first really conclusive evidence that things are changing in men's tennis.

It was the first slam final in almost 10 years not to feature Federer, Djokovic, Rafael Nadal or Andy Murray and the first between two first-time finalists ranked outside the top 10 since Pat Rafter beat Greg Rusedski here in 1997.

Cilic had cited the inspiration he took from seeing Stan Wawrinka winning the Australian Open, and he said: "You are a lot of the time up and down.

"It's, I feel, very inspirational for all the other guys out there who are working and sometimes losing motivation, having trouble to dig deep and to believe in the achievements.

"I would definitely feel much stronger if I would see somebody like me accomplish things like this. It came out of nowhere for me."

Cilic had played the best match of his life to stun Federer in straight sets in the last four, while Nishikori outlasted Djokovic in brutally hot and humid conditions.

The final was a tough match to call at the start, but as soon as Cilic broke serve in the first set, there only looked like being one winner.

Nishikori admitted nerves had got to him, saying: "It was one of the worst matches I played, but also he was very aggressive and very fast.

"I was, I have to say, a little bit nervous - first final. But I've been very excited these two weeks. I didn't expect anything coming here. Before I was injured and had little practice.

"There are so many positive things for sure that I can take from these two weeks, beating Stan and Novak again. I'm disappointed of course today, but it's been a very good two weeks."

Nishikori, the first Asian man to contest a slam singles final, had minor surgery on his foot a few weeks before the tournament and had thought he might not be able to play at all.

A man once thought of as physically frail put that to bed decisively with back-to-back five-set wins over Milos Raonic and Wawrinka before seeing off world number one Djokovic.

But those matches took their toll and he said: "It's not always easy to play two five sets and come here to the final. Hopefully next time I don't have to play a lot of five sets. But still I beat top-five guys.

"I think I showed my potential. I can beat anybody now. So if I can keep training hard and also practice hard, I think I have more chances coming up."

Cilic's victory means Andy Murray will drop out of the top 10 for the first time in six years, with Cilic climbing to ninth, one place behind Nishikori.

PA