His next opponent is his good friend and Davis Cup teammate Janko Tipsarevic, who beat Juan Carlos Ferrero of Spain in a nearly four-hour struggle.

Tipsarevic powered his way through the match, serving up 20 aces to eight for Ferrero, tipping the scales in what was an otherwise very tightly played match.

Ferrero, a former holder of the world No. 1 ranking, was broken at 5-5 in the third set in what proved to be the turning point in the match. Tipsarevic won the fourth and final set 6-2 in convincing fashion. Fittingly, Tipsarevic took match point on his 20th ace on the day.

The win sends the 20th-ranked Tipsarevic to the first quarterfinal of his career. He entered the top 20 of the world rankings just last month.

"It means there's going to be at least one Serbian in the semifinals, which is great for our country," Djokovic said.

"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 quarterfinals and we both want to win."

Djokovic still has yet to lose a set in the tournament.

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