The Spanish clay court specialist won 6-4 3-6 6-1 against third seed Stanislas Wawrinka of Switzerland.
And he was out of sorts when losing to Stanislas Wawrinka at Flushing Meadows.
Djokovic himself needed five sets to get past Stanislas Wawrinka in the fourth round.
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In the fourth round, he won a five-hour, five-set match against Stanislas Wawrinka after trailing 6-1, 5-2.
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But there was bad news for Djokovic's conqueror, Dimitrov, who was beaten 3-6 6-4 6-1 by Stanislas Wawrinka.
Federer will next face Swiss compatriot Stanislas Wawrinka after he disposed of American Andy Roddick in straight sets.
Nadal will now face France's Jo-Wilfried Tsonga, who saw off Stanislas Wawrinka 2-6 6-3 6-4 in his quarterfinal tie.
Potential third- and fourth-round opponents Ivo Karlovic and Stanislas Wawrinka suffered surprise defeats.
The 25-year-old Djokovic will play Ukrainian 14th seed Alexander Dolgopolov, who dispatched Stanislas Wawrinka of Switzerland in straight sets.
Even then, as Stanislas Wawrinka learned this tournament, it might not be enough.
There were also victories on Tuesday for France's No. 7 seed Richard Gasquet, Stanislas Wawrinka, seeded 13 and Juan Monaco.
The winner of that match will play either big-serving American second seed John Isner or Swiss No. 4 Stanislas Wawrinka.
The tournament, which is not an official ATP Tour event, also featured Russia's Nikolay Davydenko and Federer's Swiss compatriot Stanislas Wawrinka.
In Oeiras, Stanislas Wawrinka upset top seed and world No. 4 David Ferrer 6-1 6-4 to win the Portugal Open on Sunday.
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But 14th seed Nicolas Almagro was beaten by Stanislas Wawrinka 6-3 6-3.
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Stanislas Wawrinka, rest assured, is not the greatest player to ever live.
Roger Federer struggled against Stanislas Wawrinka but prevailed (also in three sets).
There were also wins for Stanislas Wawrinka , the Swiss No. 16 seed, and Tommy Haas , the No. 13 seed from Germany.
Meanwhile, defending champion Marin Cilic will play Swiss third seed Stanislas Wawrinka in the final of the Chennai Open in India on Sunday.
The cause of his frustration seemed apparent: He was down two sets to zero to Stanislas Wawrinka en route to a 3-1 loss.
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He will play either Jo-Wilfried Tsonga or Stanislas Wawrinka in the quarterfinals (their match was suspended for darkness Sunday evening in the fifth set).
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The Spaniard, who has now reached seven successive finals since his comeback from knee injury in February, will next face Swiss 15th seed Stanislas Wawrinka.
David Ferrer beat Stanislas Wawrinka 6-2 6-4 6-0 to give Spain an unassailable lead in the World Group tie after they had led 2-1 overnight.
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At 30 years of age, he takes the silver medal, which will accompany the doubles gold he won with Swiss countryman Stanislas Wawrinka in 2008.
The Australian Open semifinalist beat compatriot Tommy Robredo 6-3 6-2 on Saturday, while Stanislas Wawrinka beat yet another Spaniard in Nicolas Almagro, winning 6-3 7-5.
No. 20 Sam Querrey advanced when fellow American Brian Baker retired in the second set with a right knee injury and next plays No. 15 Stanislas Wawrinka.
The other quarterfinal will be between 21-year-old Canadian Milos Raonic, who beat fifth-seeded Czech Tomas Berdych, and Federer's Swiss compatriot Stanislas Wawrinka -- who defeated Japanese No. 14 Kei Nishikori.
But a surprise four-set defeat by Switzerland's Stanislas Wawrinka followed in the third round at Flushing Meadows, with the Briton beset by physical issues that he was unable to explain immediately afterwards.
Seventh seed Jo-Wilfried Tsonga beat Colombian qualifier Santiago Giraldo 6-3 6-4 and will face Ferrer in the last eight, while fifth seed Robin Soderling went down 6-3 6-2 to Stanislas Wawrinka .
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