Unseeded Argentine David Nalbandian inflicted a shock 6-1, 6-2 defeat on world number two Rafael Nadal [Images] in the Madrid Masters on Friday to earn a semi-final showdown with young Serb Novak Djokovic.

Holder Roger Federer [Images] produced another polished performance to shake off Spanish wild card Feliciano Lopez 7-6, 6-4.

The world number one next plays unseeded German Nicolas Kiefer, who continued his resurgence after more than a year out with a wrist injury by defeating fifth seed Fernando Gonzalez 7-6, 6-2.

Chilean Gonzalez was beaten by Federer in last year's final.

An out-of-sorts Nadal looked to be suffering the after-effects of Thursday night's gruelling victory over Andy Murray as he surrendered his serve on five occasions, lost nine games in a row and made a host of unforced errors.

It was the Spaniard's heaviest defeat since he lost to Julien Benneteau in Lyon in Oct. 2004 when he also won only three games, and the second time in a row he has fallen in the quarters in Madrid.

For Nalbandian, runner-up here in 2004, the victory put him in the semis for the first time this year and came as a welcome boost at the end of a disappointing season in which he has dropped out of the top 10 to 25th in the world.

"Everything went right for me today," the Argentine told reporters. "I took advantage of all Rafa's errors and he never felt comfortable but I felt I played really well."

Unlike Murray, who had five early break points against Nadal, Nalbandian took his chances and broke the Spaniard in the third game.

Nalbandian broke twice more to take the set 6-1 and reeled off nine games without reply to grab a 3-0 lead in the second.

FRUSTRATED NADAL

Nadal, winner here in 2005, struggled to control his ground shots and Nalbandian stretched the Mallorcan across the court and kept the rallies going to tire out his opponent.

A frustrated Nadal slammed an easy forehand into the net as he surrendered his serve again in the second game and although he tried to pump himself up with the crowd's support, he was unable to break the Argentine's concentration.

Lopez put up a brave fight against Federer, weathering five break points in a marathon eighth game and also saving a set point, but there was nothing he could do to stop the Swiss seizing the opening set.

Federer then broke serve in the ninth game of the second as he claimed his 57th win of the year.

World number three Djokovic powered his way to a 7-6, 6-2 victory over unseeded Croat Mario Ancic. 

The 20-year-old Serb became the first player to take a set off Ancic this week before twice breaking serve in the second.

"The second set was something else, it was really good and I'm starting to feel better and better," said Djokovic.

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