Tenth-seeded Kei Nishikori of Japan advanced to the third round of the U.S. Open on Thursday when Pablo Andujar retired with an injury.

Nishikori was leading 6-4, 6-1 when the 48th-ranked Andujar suddenly came to the net. Tournament officials did not immediately detail the nature of the Spaniard's injury.

''It's unfortunate for Pablo today, but I have been playing well ... had good two sets,'' Nishikori said.

The 24-year-old Nishikori, who has never made it past the fourth round in five previous U.S. Open appearances, has been battling an injury of his own in recent weeks. A severely infected right big toe forced him to miss tuneup events leading up to Flushing Meadows.

Nishikori next faces the winner of 23rd-seeded Leonardo Mayer and Matthew Ebden.

Top-seeded Novak Djokovic won in straight sets and No. 9 Jo-Willfried Tsonga, advanced easily. 

Djokovic danced for the fans, doing a sort of salsa to Iggy Azalea's summer hit "Fancy," after his 6-1, 6-3, 6-0, rout of Frenchman Paul-Henri Mathieu.

Djokovic next faces American Sam Querrey, who downed 28th-seeded Spaniard Guillermo Garcia-Lopez in straight sets.

Cramp-free on a cool summer's night, Andy Murray moved easily into the third round owith a 6-3, 6-3, 6-4 victory over Matthias Bachinger.

The eighth-seeded Murray, who battled cramps in his hamstring, shoulder and arm during a four-set win over Robin Haase in the heat of the day Monday, showed no such trouble on a crisp, 75-degree night in Arthur Ashe Stadium.

Murray, the 2012 U.S. Open champion, has not reached a final since winning Wimbledon in 2013. He next faces Andrey Kuznetsov of Russia. 

The only seeded American, No. 13 John Isner, slammed 30 aces and 54 winners in a straight-set victory over German Jan-Lennard Struff.

American Sam Querrey downed 28th-seeded Spaniard Guillermo Garcia-Lopez in straight sets and two seeded players, No. 10 Kei Nishikori and No. 22 Philipp Kohlschreiber, advanced to the third round when their opponents retired because of injury. No. 9 Jo-Willfried Tsonga also advanced in straight sets.