Result: Novak Djokovic secures quarter final place

World number one Novak Djokovic has assured himself a place in the quarter final of the US Open after a straight-sets victory over Ukraine's Alexandr Dolgopolov.

The match's high drama came in the first set tiebreak, during which the pair battled through five set points before the Serb triumphed 14-12.

Djokovic went on to take the following two sets relatively comfortably, 6-4 and 6-2 respectively, to seal the win.

"I was able to turn it around. It wasn't a great performance from my side in the first set, so I have to give credit to Alex," he said afterwards.

Djokovic now faces fellow Serb Janko Tipsarevic in the final eight.