First Set - 

World number one Novak Djokovic was given a torrid time by Ukrainian Alexandr Dolgopolov, but managed to come out victorious in a thrilling encounter. It ended 7-6 (16-14) 6-4 6-2 to Djokovic, and he will face fellow-Serb Janko Tipsarevic in the quarters after he defeated Spain's Juan Carlos Ferrero 7-5 6-7 (3-7) 7-5 6-2.

It was the 24-year-old's 61st win in 63 matches this year, but he's had far easier encounters during the course of his dream-season.

At the Louis Armstrong Stadium, the 22nd seed Dolgopolov's caused the Serb problems aplenty with his sliced backhand and the first set was a real thriller. The two exchanged breaks of serve, and eventually, it went down to a tie-breaker.

Dolgopolov seemed to be in total control when he went 4-0 up but when the net cord gave Djokovic a helping hand, the Serb launched his comeback. After some real eye-popping tennis, the first seed took the set although he had to save four set points and saw five set points of his own saved.

The second and third sets were straightforward though, as Djokovic broke at the start of each to register a straight-sets win that which seemed doubtful during the 75 minutes of the first set.

Winning it was very important, Djokovic said of the tie-break afterwards. That was probably the turning point. After that it was a good performance.

He played a lot of low balls, slices - I was confused on the court. But it was really exciting.

Djokovic will next face his Davis Cup teammate Tipsarevic in the quarters.

It means there's going to be at least one Serbian in the semi-finals, which is great for our country, said Djokovic. I think this is the first time I play Janko in a Grand Slam. We are great friends. It's not going to be easy to play him, but look, it's the quarter-finals and we both want to win.

If both Djokovic and Federer get through their quarterfinal encounters, they will meet in the semifinals of the tournament.