Such was the meltdown for the defending US Open champion as he crashed out of the US Open on Thursday, with Swiss ninth seed Stanislas Wawrinka dumping the British third seed 6-4, 6-3, 6-2 without even facing a break point.

The 26-year-old Scotsman had been enjoying a dream run with 2012 London Olympic gold, his first Grand Slam victory at last year's US Open and a long-sought Wimbledon triumph two months ago.

Beyond the mental burden and physical toll of his greatest Grand Slam success, Murray raised expectations after becoming the first British man since Fred Perry in 1936 to win the Wimbledon singles crown.

"I don't know if I'm meant to win every Grand Slam I play or be in the final," Murray said. "It's just very, very difficult just now. With the guys around us, it's very challenging."

Wawrinka sent Murray crashing out to reach his first Gramd Slam semi-final without facing a break chance, only the second time in 146 Slam matches that Murray could not manage a break-point against a rival.

"I didn't get into enough return games, which is disappointing," Murray said. "That's normally something I do pretty well. I always give myself opportunities to break serve, and I didn't today."

The emotional finish of closing out Wimbledon, Murray feeling the hopes of his homeland and the weight of history as he tried to finish off world number one Novak Djokovic, has made it tougher in the weeks since.

"It has been challenging both ways for different reasons," Murray said. "Physically I played some extremely tough matches in that period.

"Mentally, as well, it was very challenging for me to play Wimbledon, the last few games of Wimbledon to you guys may not seem like much, but to me it was extremely challenging."

"Mentally, in terms of the matches I played, a lot of work goes into not just those matches but the work you do to get yourself ready for them as well. It's tough."

Achieving that goal only made defending his first Slam crown that much tougher.

"When you work hard for something for a lot of years, it's going to take a bit of time to really fire yourself up and get yourself training 110%," he said.

"That's something I think is kind of natural after what happened at Wimbledon.

"But I got here. I've been here nearly three weeks now. I practiced a lot and played quite a lot of matches as well. So I gave myself a chance to do well because I prepared properly.

"I don't think I was playing poorly. I got to the quarterfinals of a Slam, which isn't easy. I would have liked to have played a little bit better. It's a shame I had to play a bad match."

The new experience of trying to defend a Slam title, something he will face again in 10 months at Wimbledon, was not a factor in the defeat, Murray said.

"No, I don't think so. I would have thought maybe at the beginning of the tournament that would have been the case, but that had zero bearing on today's match. I handled it OK," Murray said.

"It was a new experience for me and something that was good to go through, and I will learn from that for next time."

Murray was not ready to let a disheartening end spoil his memories of a special past 13 months.

"I lost in straight sets, so that's disappointing. I would have liked to have gone further," Murray said.

"But look, I can't complain. If someone told me before the US Open last year I would have been here as defending champion having won Wimbledon and Olympic gold, I would have taken that 100%.

"So I'm disappointed, but the year as a whole has been a good one."