U.S. Open: Djokovic advances as Wawrinka retires
Djokovic was leading 6-4, 6-1, 3-1 on Wednesday when Wawrinka ended the match. It was not immediately clear why he couldn't continue.
The second-seeded Serb was up 2-0 in the first set Tuesday when play was suspended because of rain. He spent a total of just 93 minutes on court to reach his 14th consecutive Grand Slam quarterfinal.
Wawrinka, seeded 18th, has lost 19 straight matches against top-three opponents.
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