Rafael Nadal's miserable year continued as the 14-time major champion threw away a two-set lead to lose to Italy's Fabio Fognini at the US Open.
Nadal outplayed Fognini for over an hour under the lights of Arthur Ashe Stadium but the Italian found a different gear as he came storming back to win 3-6 4-6 6-4 6-3 6-4.
It means Nadal has only managed to reach two quarter-finals at grand slams this year and ends the season without a major title for the first time since 2004.
The Spaniard had been bullish about a return to form in the build-up to Flushing Meadows, insisting criticism had been exaggerated for a player still ranked number eight in the world.
Fognini, however, exposed his opponent's weaknesses with devastating efficiency, unleashing 70 winners - 34 of them forehands - during an exhilarating contest which lasted three hours and 46 minutes.
The match came to a climax in the fifth set as the pair exchanged seven consecutive breaks of serve and a series of thrilling points, which had the remaining crowd applauding on their feet.
Leading 5-4, Fognini finally held serve to seal victory and the world number 30 will now face Spain's Feliciano Lopez for a place in the quarter-finals.
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"Everything I was working for and dreaming about came today," Marin Cilic said after his US Open win.
Cilic, who did not lose a set in his final three matches, said: "I think this is all the hard work in the last several years and especially the last year.
"My team brought something special, especially Goran [Ivanisevic]. The most important of all the things he brought to me was enjoying tennis and always having fun.
"I enjoyed my best tennis over here and played the best tennis of my life."
Marin Cilic crushed Japan's Kei Nishikori 6-3 ,6-3, 6-3 in the US Open final to become the first Croatian to win a Grand Slam title in 13 years.
Cilic's victory was sweet redemption after he had to sit out last year's tournament while serving a four-month doping ban.
Andy Murray suffered his worst grand slam defeat since losing to Stanislas Wawrinka in the third round in New York three years ago.
Speaking at post-match press conference a visibly disappointed Murray said: "I don't think I was playing poorly. I got to the quarter-finals of a slam which isn't easy.
"I would have liked to have played a little bit better but I've had a good run the last couple of years. It's a shame I had to play a bad match today."
Reigning US Open champion Andy Murray crashed out of this year's tournament in the quarter-finals after suffering a defeat in straight sets to Switzerland's Stanislas Wawrinka.
The ninth seed beat Britain's number one 6-4 6-3 6-2.
Andy Murray is fighting to stay in the US Open after losing the first two sets of his quarter final match against Switzerland's Stanislas Wawrinka.
The defending champion lost the opening two sets 6-4 6-3.