Del Potro crashes then smashes way to showdown with Djokovic

Both men arrive in the last four without having dropped a set, but for a while it seemed as though Del Potro's first-ever Wimbledon quarter-final wouldn't get beyond a solitary game. The Tower of Tandil was stretching those giant legs as he chased a ball beyond the baseline when he slipped and crashed to earth, his entire weight landing awkwardly on a left knee already heavily strapped after a similar mishap against Grega Zemlja of Slovenia.

Cue a pregnant pause to see if the match could continue, the All England Club presumably checking their insurance premiums before the doctor administered some anti-inflammatories and told him his only option was to run it off. Little did most of us suspect then that the 2009 US Open champion would gingerly pick himself up to his full height again and do precisely that. The 6-2, 6-4, 7-6 (5) win which booked his first grand slam semi-final since his Flushing Meadows victory – and avenged a defeat to the Spaniard here last year – proved to be the perfect medicine.

The Argentine admitted last night he was on the verge of throwing in the towel. "I was close to retiring," Del Potro said. "I was worried because it was the same movements as four days ago. The doctor says they can't do any more with my knee. I had a very tight tape, and that helped me to move a little bit, but nothing more. I took some anti-inflammatories, but it was painful at the beginning. I had just started the match and many things come to my mind, many bad things. But I tried to be positive and played unbelievable tennis. I didn't want to retire in the quarters at Wimbledon against David Ferrer, you know. That was why I continued to play. I broke his serve early and this give me confidence to take advantage."

Having outlasted the man who will rise to new heights of world No.3 next week – even if he himself was battling toe and ankle injuries – Del Potro went off into the night knowing he is back into the "fight again with the top guys", but the only problem is the form of the man he will face tomorrow. Djokovic wasted four break points in the first set and was broken twice in the second, but generally this was a composed performance against the giant Czech.

Berdych, the No.7 seed, had prevailed during their last meeting on tour and had taken the Serb's scalp during Wimbledon 2010, but the loss of the second serve from a winning position was a hammer blow en route to his 7-6 (5), 6-4, 6-3 defeat.

It all set up Djokovic's 13th successive grand slam semi-final, even if the Serb joked that it isn't quite up there with the 23 Roger Federer managed between 2004 and 2010. He said he had been inspired by the presence of watching Serbian football star Nemanja Vidic, and had played so well that he would make sure that the Manchester United defender would also attend his semi-final, not that the 26-year-old has been struggling too much in his absence.

"We wanted to invite Nemanja because he's one of the most successful and most recognised Serbian people in the world," said Djokovic, who is involved with a charity foundation with his fellow Serb. "It's the first time he has come to watch me. He's a lucky charm. I'll make sure he's there."

While Del Potro was crashing to earth, Djokovic was displaying once more that fearsome flexibility, sliding on grass to the extent that at one point he was in a full splits position. "I have had nasty falls also," the Serb said. "On the grass it is not necessary too much to slide. But I do slide on some balls and sometimes it helps me, you know, to recover better, to defend better. It's the way I have been moving all my life."

Tomorrow's encounter is enlivened still further by the fact that Del Potro was the victor when the two men last met on this patch of South West London, taking the Olympic bronze medal match 14-12 in the final set. Del Potro said he wouldn't risk his battered body to play, and would need to be "100% or even 110% against him". Time for another dose of those magic pills.