Sept. 2 (UPI) -- Top men's seed Novak Djokovic pulled out of the 2019 U.S. Open in the third set of his round of 16 match against Stan Wawrinka due to a shoulder injury, allowing his Swiss foe to advance to the quarterfinals.
Djokovic -- the No. 1 player in the world -- lost the first set 6-4 and the second set 7-5 Sunday at Arthur Ashe Stadium in Queens. The Serb was losing 2-1 in the third set, before withdrawing the match. Warinka battles Daniil Medvedev in a quarterfinal matchup Tuesday at Flushing Meadows.
Djokovic was the defending champion in the men's singles circuit of the Grand Slam. The winner of the Wawrikna and Medvedev matchup faces Roger Federer or Grigor Dimitrov for a chance to play in the 2019 men's final.
"I congratulate Stan," Djokovic told reporters. "He's a great player. I really want to wish him all the best the rest of the tournament. I don't want to talk about my injuries."
Wawrinka was mostly-dominant throughout the match, with the exception of Djokovic's early 3-0 lead in the second set. Djokovic had an uncharacteristic 35 unforced errors in the match, compared to Wawrinka's 19 unforced errors. Wawrinkna also had nine aces in the win.
Djokovic fired a double fault by hitting a serve into the net in the third set. He shook his head as he walked off the court and embraced Wawrinka before retiring. Djokovic was looking to win his third Grand Slam of 2019, after capturing titles at the Australian Open and Wimbledon.
"It's very special to play the No. 1 player in the world. Sorry he had to retire to finish the game like that," Wawrinka said.
Wawrinka said he was surprised Djokovic retired. The crowd in Queens booed as Djokovic left the court.
"I'm sorry for the crowd, obviously they came to see a full match and it just wasn't to be," Djokovic said. "A lot of people didn't know what was happening so I can't blame them. But it is what it is."
Wawrinka, 34, won the 2016 U.S. Open. He is a three-time Grand Slam champion.
"[Stan] is a big matches player," Djokovic said. "He loves to play on the big stage against the best players in the world. It is what has gotten him three Grand Slams and Olympic gold and everything ... It's great to see him playing at the highest level.