Andy Murray believes his US Open defeat to Marin Cilic was the biggest disappointment of his career.

Second seed Murray had been strongly tipped to go one better than 2008 at Flushing Meadow, when he reached a first Grand Slam final only to lose to Roger Federer.

But the British number one seemed out of sorts against Croatian Cilic in their fourth round encounter, going down tamely 7-5, 6-2, 6-2.

"Was it the biggest disappointment of my career, yeah - although worse things have happened to me," said Murray,

"The way the match went was just disappointing.

"I don't know why it happened, which makes the defeat even more upsetting.

"I just didn't find a way to get myself into the game and I just allowed him to dictate the play."

Murray refused to blame a wrist problem that seemed to be troubling him before and after the match - and vowed to end the season strongly, with the ATP Tour Final - being staged in London for the first time - his main target.

"Regardless of my wrist, I lost the match. I returned poorly and he served well - that was really the difference," he added.

"I just couldn't get myself into enough return games to get myself back into the match.

"A lot of times when I lose I get asked 'why did you look flat?' but it is not always the case. I couldn't get myself into games and he was dominating points so there wasn't much I could do about it.

"I believe that I'll come back better from this. I'll learn a lot from what happened this week, like I have usually done when I've had bad results.

"I'll come back better and stronger."

Match report

Anguished Andy Murray crashed out of the US Open with a humbling straight sets fourth round defeat in New York.

In a season of breakthroughs that has seen him scale the world rankings, this will be a bigger disappointment than his semi-final loss to Andy Roddick at Wimbledon, due to the tame nature of his performance on his favoured surface.

The British number one and second seed seemed out of sync and rhythm as he was outfought and outthought by Marin Cilic, going down 7-6, 6-2, 6-2 in just two hours and eight minutes.

Murray had won his three previous encounters with the six foot six inch Croatian - breezing past him in straight sets at the same stage of the French Open at Roland Garros earlier this year.

But 20-year old Cilic produced the performance of his career - reaching the last eight of a Grand Slam for the first time ever.

Murray had his chances - and will rue a series of squandered break point opportunities in a close fought first set.

However, no-one will argue that Cilic wasn't value for his progress as the Scot paid the ultimate price for a passive and tense display.

Last year's finalist seemed to be struggling with his left wrist and was spotted receiving treatment from physio Jez Green during his warm-up at Flushing Meadow.

And, as he tossed his sweatbands into the crowd after marching off the court, he revealed strapping on the apparent problem.

Twelve months ago he came from two sets down to beat Jurgen Meltzer - igniting a run that took him to a maiden Grand Slam final.

However, this time around he simply had no answer to the questions asked by a determined Cilic, who will now face Juan Martin Del Potro, following his 6-3, 6-3, 6-3 win over Juan Carlos Ferrero.