LONDON -- The spectators were still settling into their seats when Juan Martin del Potro chased an overhead into the corner, only to feel his foot go out from under him on Wimbledon's slick grass. Del Potro's knee straightened suddenly, then bent backward. The 6-foot-6 Argentine crumpled to the ground and rolled twice into the far edge of Centre Court.
Only five points into Wednesday's quarterfinal, the match appeared over before it had really gotten going.
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No such luck for his opponent, David Ferrer.
First at a limp, then at a jog, then at a sprint, del Potro recovered for a 6-2, 6-4, 7-6 (5) victory over the fourth-seeded Ferrer to make his first Wimbledon semifinal. His opponent will be top-seeded Novak Djokovic, whose 7-6 (5), 6-4, 6-3 victory over No. 7 Tomas Berdych ended less than five seconds after del Potro hit his final shot.
"It's really, really painful," del Potro said of the injury that has been bothering him since he first slipped on the turf last Saturday. "I twist my knee once again, but the doctor gave me some magic pills. I could finish the match. I'm so glad to go through."
During a tournament with more than its share of twists and turns -- to say nothing of slips and slides -- Djokovic and del Potro have gone through virtually unscathed, on the scoreboard at least. Neither man has dropped a set.
Djokovic overcame a two-break, 3-0 deficit in the second set to cruise to his latest victory over Berdych, the 2010 Wimbledon runner-up. Djokovic is in his 13th straight Grand Slam semifinal and in search of his seventh major title.
No. 8 del Potro, meanwhile, is starting to show the form he used to win his only major championship, the U.S. Open in 2009. He's 3-8 lifetime against Djokovic, though one of those victories came here, at the All England Club, when he beat the Serb in the Olympic bronze-medal match last year. Del Potro also won their last meeting, earlier this year on hard court at Indian Wells.
He has been wracked with pain through most of his stay here at Wimbledon, where the slickness of the grass has created its share of complaints.
But del Potro wasn't the only one hurting Wednesday.
Ferrer has also been dealing with ankle and toe issues. He cut short his pre-match hitting session because of pain in his ankle but said that was no excuse. Ferrer, who crossed the net to run toward del Potro to check on him when he fell, said he didn't see much change in his opponent's play after the injury.
"Juan Martin, he was more focused, he was playing more aggressive than me and he served very, very good in all three sets," Ferrer said.
Soon after his match, del Potro had an appointment with an ice tub and his trainers. His knee, mummified with athletic tape even before he went down in Wednesday's match, needs work. But if the doctors can patch him up, he's certainly playing some of his best tennis.
"In the end, I played my best forehand ever this Wimbledon," said del Potro, who hit 42 winners against only 11 unforced errors.
Djokovic has been feeling pretty good about his game, as well. He had 36 winners and 13 unforced errors against Berdych.
"I've been playing my best tennis of the year on grass," Djokovic said. "I'm glad because it's not my most preferred surface. Hopefully, my experience can help me."
After their matches ended, the next two quarterfinals began -- one pitting second-seeded Andy Murray of Britain against Fernando Verdasco of Spain, the other an all-Polish affair, with Lukasz Kubot going against No. 24 Jerzy Janowicz, with the winner to become the first Polish semifinalist in Grand Slam history.