Novak Djokovic’s US Open title defence came to a halt on Sunday when the Serb retired from his fourth-round match against Stan Wawrinka due to a shoulder injury.
Novak Djokovic and Roger Federer remain on a collision course to meet in the US Open semi-finals after they each claimed straight-sets wins to reach the last 16.
Serena Williams will resume her quest for a record-tying 24th Grand Slam title at the US Open on Wednesday while holder Novak Djokovic and five-times champion Roger Federer also seek passage to the third round.
Novak Djokovic was all set to cruise into the U.S. Open as hot favourite but a semi-final defeat at the Cincinnati Masters last week has at least given hope to his challengers that the world number one is not invincible.
World number one, Novak Djokovic, is one of only four seeded players who made it to the quarter-finals of the Cincinnati Masters tennis tournament.