Novak Djokovic of Serbia lunges to make a return to compatriot Janko Tipsarevic during their match at the U.S. Open tennis tournament in New York. Picture - Reuters.

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In one of just two quarterfinals played on Thursday, as the bottom half of the men's draw has been delayed due to rain, world number one Novak Djokovic was adjudged the victor after fellow-Serb Janko Tipsarevic retired with a leg-injury.

The top seed didn't look at his best, and was given a torrid time from his fellow-countryman. On one occasion, he allowed Tipsarevic to fight back from 5-2 down and serve for the first set although he did manage to level scores and push it into a tie-breaker in which he strolled.  

The second set went down to a tie-breaker too, with Tipsarevic leveling at one-set all.

However, Djokovic came powering back in the third although Tipsarevic did require treatment for an injury to his leg. Djokovic also needed medical attention due to a bleeding toe. Eventually, it was Tipsarevic who retired hurt at 7-6 (7-2) 6-7 (3-7) 6-0 3-0.

My left toe is bleeding, said Djokovic afterwards. These things happen all the time when you're sliding like I do.