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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Serena Williams in U.S. Open quarterfinals

Serena Williams fought off the wind, along with brief flurries of effectiveness from her opponent, to advance to the quarterfinals of the U.S. Open with a 6-3, 6-4 victory Monday over Ana Ivanovic.
Williams closed the match with four straight serves that Ivanovic couldn’t return – clocked at between 99 and 111 mph in a blustery Arthur Ashe Stadium that had both players fighting with their tosses and topspin.