Novak Djokovic of Serbia serves to Jerzy Janowicz of Poland on day one of the 2016 US Open tennis tournament at USTA Billie Jean King National Tennis Center in New York, US, on August 29, 2016. [Photo/Agencies]

World number one Novak Djokovic received a free pass into the third round of the US Open when Jiri Vesely of the Czech Republic withdrew from their match on Wednesday due to a left forearm injury.

The walkover provided the top-seeded defending champion with an extended break to improve his niggling left wrist injury before his next match against either Guido Pella of Argentina or Mikhail Youzhny of Russia.

The 23-year-old Vesely, ranked 49th, beat Djokovic in the second round at the ATP Masters 1000 Monte Carlo event in April in their only meeting, making him one of two top 100 players with more wins than losses against the Serbian.

World number 23 Ivo Karlovic is 2-1 head-to-head against Djokovic.