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* Djokovic edges epic five-setter
* Longest Wimbledon semi-final
LONDON, July 5 (Reuters) - In the end, an exhausted, sweat-soaked Novak Djokovic could not stop himself from joining 15,000 hollering fans in giving Argentine warrior Juan Martin Del Potro a standing ovation after an epic display of courage and endurance at Wimbledon on Friday.
A contest that many feared would last only a few minutes after Del Potro damaged his knee so badly that he came close to quitting two days ago, went into surreal territory as Djokovic relied on his survival instincts to reach the final with a rousing 7-5 4-6 7-6(2) 6-7(6) 6-3 win.
At four hours 43 minutes, it was the longest semi-final ever played at the All England Club and while the scoreline showed that the Serbian world number one had set up a final date with Andy Murray, for all those lucky enough to on Centre Court, there were no losers.
"It was one of my best matches I've been a part of, one of the most exciting. It was so close," the 2011 champion said after being stretched to his fifth five-hour marathon within the space of 18 months.
"I could not separate us. That was one of the best matches I've played here, it was at such a high level. I'm just privileged to be the winner of this match."
Del Potro's gutsy display won him a new legion of global fans but that was little consolation for the eighth seed as for the second time in less than a year, he suffered a heartbreak of epic proportions on Centre Court.
Eleven months after falling to Roger Federer in the Olympic semi-final, which ended 19-17 in the third set after four hours 26 minutes, Del Potro was again left deflated.
"It was unbelievable to watch but, of course, I'm sad because I lost and I was close to beating him," said the man nicknamed as the Tower of Tandil.
A man who lay on the famous green turf writhing in pain just five points into his quarter-final against David Ferrer seemed to have emerged with a bionic left knee on Friday, albeit heavily strapped.
If Djokovic had hoped to inflict more pain on Del Potro and quickly deliver the killer blow in the semi-final, he was in for a rude shock.
Instead, it was Djokovic who was left with battered knees, sore elbows and a bruised stomach as Del Potro's brutal forehand sent him diving and lunging around court - often in vain.
So monstrous was Del Potro's forehand that it often produced a murderous thud as it flew off his racket. If there was a speed gun around to measuring the velocity of his forehand, it would probably have been off the radar.
The sixth game gave a taster of what was to come as it featured a scorching 24-shot rally, five deuces, two double faults, one break point before the Argentine answered a booming cry of "Come on Del Boy" to hold on.
Djokovic finally broke in the 12th game of the first set to win it 7-5 after 55 nerve-jangling minutes.
When the Argentine called on the trainer while trailing 3-2 in the second set, alarm bells started to ring, and they got even louder in the next game as he fell 15-40 behind.
But the Serb fluffed his lines as he wasted four break points and astonishingly got broken to love in the next game as Del Potro nosed 4-3 ahead.
That allowed him to level the match and if the first two sets were not dramatic enough the crowd demanded more.
After seeing a "Mr Serious" Del Potro in the first set, and a "Mr Cool" Del Potro in the second, it was time for "Mr Funny" Del Potro to take charge in the third.
He ran on top of the side barriers and, arms flailing, threatened to fall into the lap of a bemused female fan as he took a breather following one gruelling exchange.
It was no laughing matter, though, when Djokovic, after watching three set points vanish at 6-5, romped through the tiebreak and took it 7-2 by clubbing a backhand winner.
In a battle featuring one sinew-stretching rally after another, the top seed broke in the seventh game of the fourth set but Del Potro broke straight back to extend it into a tiebreak.
At 5.04 pm local time, with the help of an astonishing reflex volley winner, Djokovic earned two match points at 6-4 in the breaker.
But Del Potro survived a heart-pumping 25-shot rally and waving his arms above his head, he shooed out Djokovic's final lob over the baseline.
When a screaming forehand winner made it 6-6, the crowd erupted and two points later they could be heard all around the southwest London when a backhand error from Djokovic made it two sets all.
A match that was supposed to be a curtain-raiser for the second semi-final between home hope Murray and Poland's Jerzy Janowicz was now a Wimbledon classic and the fans were on the edge of the seats waiting to see how the fifth act would play out.
Djokovic finally ended Del Potro's brave resistance by breaking for a 5-3 lead and was a hugely relieved man when he clinched victory with a searing backhand winner.
Among those giving the players a prolonged standing ovation was twice former champion Stefan Edberg, who holds the record of winning the longest ever grand slam semi-final, a five hour 26 minute duel against Michael Chang at the 1992 U.S. Open.
"I know I was pushed to the limit today," said Djokovic, who is unlikely to forget the 22 aces and 80 winners he produced during the most thrilling match of the 2013 championships. (Editing by Ed Osmond)