US Open: No. 1 seed Novak Djokovic's title defence ends in fourth round

Djokovic, who won four of the last five Grand Slam titles, decided to not continue the game and walked off the court in the third set.

New York: Defending champion and world number one Novak Djokovic retired from the round of 16-match against Stan Wawrinka in the ongoing US Open after he suffered a shoulder injury in his left shoulder.

After losing the first two sets by 6-4, 7-5, Djokovic was trailing by 2-1 in the third set against Switzerland's Wawrinka at Arthur Ashe Stadium.

Djokovic, who won four of the last five Grand Slam titles, decided to not continue the game and walked off the court in the third set.

"It's never the way you want to finish a match. I feel sorry for Novak. He's a friend and an amazing champion. We've played some amazing battles all my career," Association of Tennis Professionals (ATP) quoted Wawrinka as saying after the match.

Wawrinka will now face Russian fifth seed Daniil Medvedev in a quarterfinal match on September 3.