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Roddick shock as Lu through

Andy Roddick pointed to three "horrendous" sets as the reason for his shock capitulation against Taiwan's Yen-Hsun Lu in the fourth round of Wimbledon yesterday.

Lu caused the biggest upset at this year's tournament by defeating the three-time finalist 4-6 7-6 (7/3) 7-6 (7/4) 6-7 (5/7) 9-7 in the fourth round.

Despite winning the opening set, Roddick was out of sorts as he slumped to back-to-back tie-break losses to hand the world No82 the initiative.

"Through three sets I was playing horrendously. Really, really badly, to the point where I was thinking how to put balls on the court," said the fifth seed.

"I think the fifth set was the best I played in terms of hitting the ball. But when you dig yourself a hole it's tough to get out when you've given someone confidence and when they have their feet under them a little bit more."

The American was asked whether he was stunned by the outcome.

"I don't think stunned is the right word," Roddick said. "I don't view what happened as an impossibility.

"I don't know. I always struggle with how to describe my mood.

"He deserved to win more than I did, that's for sure."

Lu will face Novak Djokovic in the quarter-finals on Wednesday having never previously gone past the second round at Wimbledon.

Third seed Djokovic progressed after seeing off 2002 champion Lleyton Hewitt in four sets.

Top seed and defending champion Roger Federer defeated Jurgen Melzer to tee up a last-eight clash with Tomas Berdych, who defeated Germany's Daniel Brands in four sets.

Federer's victory in three sets was just the tonic after a tough opening week at SW19 which saw him taken to five sets in the opening round and four in the second, and he was pleased with the progress shown yesterday.

"I thought I played great," Federer said. "Aggressive right from the start, which I think was key."

Elsewhere yesterday, Rafael Nadal and Robin Soderling set up a mouthwatering quarter-final clash with contrasting last-16 wins.

Nadal posted a dominant straight-sets victory over Paul-Henri Mathieu while Soderling saw off David Ferrer in a gruelling five-setter.

Andy Murray reeled off his fourth consecutive straight-sets win to reach the last eight, beating Sam Querrey 7-5 6-3 6-4 in a little over two hours.

Jo-Wilfried Tsonga, the 10th seed, is next up for Murray after a four-set win over fellow Frenchman Julien Benneteau.

Robin Soderling's passage into his first Wimbledon quarter-final yesterday was anything but smooth and was almost upset by a sick ball girl.

With the Swede serving for the match at 40-15, play was halted when a ball girl, appearing to suffer the effects of the heat, was led off court.

Soderling failed to convert two match points before Spaniard David Ferrer hit a return long on the third to give the sixth seed a 6-2 5-7 6-2 3-6 7-5 victory on tiny Court 12.

"All of a sudden they stopped play, and then I understood she didn't feel well. Must be tough for them to stay out there for so many hours," Soderling said. "I hope she's fine. It was just pretty bad timing, me serving for the match at match point. It could have happened a little bit earlier. But that's how it is. I hope she's fine now."