World number one, Novak Djokovic, would not be defending his US Open title, after he was forced to retire in his fourth round clash against Stanislas Wawrinka on Sunday.
The Serb abandoned the match due to a shoulder injury being two sets and a break down against the Swiss.
The 32-year-old had showed signs that his title defense could be in jeopardy, after he required a lengthy treatment on his left shoulder in the second round against Juan Ignacio Londero, which he won.
But there was no way back for him against Wawrinka, a much tougher opponent.
Wawrinka, who will next face Daniil Medvedev in the quarter-final, deserves credit for his performance. His one-handed backhand was well hit with great force, and he served well under pressure.
Djokovic was booed by fans as he was leaving the Arthur Ashe court, a gesture he returned with a sarcastic thumbs up.