World number one Novak Djokovic is out of the US Open after retiring with an injury in his fourth round clash with Stan Wawrinka.
The Serbian was already trailing by two sets to the 34-year-old, who was playing phenomenally, after being hampered by a shoulder injury.
But he decided to walk off court two hours into his match on Arthur Ashe, a move that stunned the crowd and pundits alike.
Djokovic received treatment from the medical trainer on court during his round two match with Juan Ignacio Londero before going onto win.
The 32-year-old was forced to undergo more treatment when two sets down to Wawrinka but succumbed to the pain after failing a break behind in the third set.
The decision was met by a chorus of boos from the crowd, who had supported the 23rd seed more throughout the evening.
The retirement means Wawrinka advances to the quarter-finals while Djokovic gives up his US Open title.
