Novak Djokovic : No Problems For No. 1 At U.S. Open 2011

NEW YORK -- Top-ranked Novak Djokovic survived a marathon tiebreaker then cruised the rest of the way to beat Alexandr Dolgopolov in the fourth round of the U.S. Open.

The Serb won 7-6 (14), 6-4, 6-2 on Monday. He'll face countryman Janko Tipsarevic in the quarterfinals.
Djokovic fought off four set points in the tiebreaker against the 22nd-seeded Ukrainian. He finally clinched the set with a big serve.

Djokovic needed 76 minutes to win the first set and a combined 70 to take the last two.
Djokovic fell behind 0-4 in the tiebreaker but regained momentum when his shot ticked off the top of the net and over, and Dolgopolov's backhand crosscourt volley landed just wide.

The 22-year-old Dolgopolov reached the quarterfinals at this year's Australian Open.

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