Djokovic is the first player to beat Nadal twice on the Roland Garros clay, also beating him in the 2015 quarter-finals
Novak Djokovic ended Rafael Nadal's reign at the French Open with a four-set win in a classic semi-final which will be ranked among the all-time great matches on the Roland Garros clay.
Serbian top seed Djokovic won 3-6 6-3 7-6 (7-4) 6-2 against Nadal, champion in each of the past four years.
Nadal, going for a record-extending 14th title, lost at Roland Garros for only the third time in 108 matches.
Djokovic, 34, must now recover to play Stefanos Tsitsipas in Sunday's final.
The 22-year-old Greek reached his first Grand Slam final by beating German sixth seed Alexander Zverev in a five-set epic earlier on Friday.
Fifth seed Tsitsipas must surely have been watching, like the rest of the tennis world was, as two of the all-time greats fought out a brutal battle for the right to face him in the showpiece.
"It was one of these matches you can remember forever. It was one of the top three matches in my life," said Djokovic.
The high-quality match was full of drama and suspense, twists and turns, as it was played in front of 5,000 fans, who were allowed to stay despite France's 11pm curfew as part of its coronavirus restrictions.
That decision came after a remarkable 98-minute third set which saw Djokovic hold his nerve to win a tie-break on which the whole match seemed to hinge.
Spaniard Nadal, 35, did break serve in the first game of the fourth set and led 2-0, but could not cope with Djokovic's sky-high level as he quickly won the next six games to wrap up victory after more than four hours on court.
Djokovic looked shattered as he raised his arms in celebration, then wearily broke into a smile as he prepared for the on-court interview given by the winner.
"To win against Rafa on this court you have to play your best tennis, and tonight I played my best tennis," said Djokovic, who could now win his 19th Grand Slam title to move one behind Nadal and Federer's all-time record.
"It's hard to find the words to sum up how I feel. You tell yourself there is no pressure but there is. Pressure is a privilege – to test my game and my character in matches like this."
Djokovic's victory extended his advantage in the head-to-head with Nadal, having claimed his 30th win in their men's record 58th meeting.
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Djokovic maintains composure as he recovers from slow start
Beating Nadal on the Roland Garros clay is widely considered one of the toughest tasks in sport, but if anyone was going to achieve that this year then it felt like Djokovic was the man to do it.
The world number one had been hitting cleanly and precisely throughout the tournament, moving well and playing aggressively on his way to the last four.
Nadal blew Djokovic away in a fast start when they met on Chatrier in October's final and, after seeing off two break points in a nine-minute opening game, again managed to get the scoreboard quickly moving in his favour.
Unable to find his rhythm, or his touch with some early drop-shots, Djokovic fell 5-0 behind in another extraordinary start which few would have expected.
Djokovic saved the bagel with a hold, settling down further to get one break back but was unable to nab another.
Nadal served out at the second time of asking, taking his seventh break point of an enthralling first set lasting almost an hour.
The ferocity of the exchanges continued in an equally exhausting second set.
Djokovic was unable to consolidate an early break at 2-0, but did back up another in the sixth game with a mammoth hold where he saved three break-back points.
Pressure told when Djokovic attempted to serve out the set, producing a double fault to give another break-back point to Nadal.
The Serb was let off the hook when Nadal batted a return long and saved another on his way to restoring parity at one-set all.
Gripping third set turns match into 'one of the best ever seen'
Then came a third set described by former professionals, seasoned journalists and engrossed fans as one of the greatest ever seen.
In an electric atmosphere on Chatrier, Djokovic broke for 3-2 and then immediately came back under pressure from Nadal.
The Serb saved a second break point following a 23-shot rally, then whipped up the crowd by asking them for more support.
However, he could not deny Nadal a third. Djokovic looked stunned when the left-hander whipped a forehand winner down the line for the instant break back.
That left the score at 6-3 6-3 3-3, with both men having won 84 points each, after more than two-and-a-half hours on the clock.
The quality brought an incredulous reaction from British former world number one Andy Murray on Twitter:
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The expenditure of energy in taking Djokovic's serve again came at a cost for Nadal, though.
The 13-time champion surprisingly lost his next serve to love and, even though he created a break point himself in the next game, could not convert a fourth successive break.
Tension was high on the court and in the stands, where fans regularly leapt to their feet for standing ovations and chanted the names of both players.
After Djokovic was unable to serve out the set at 5-4 and was broken, Nadal saved two more break points in the next game for a 6-5 lead.
At various points, both players cathartically released some of the stress with explosive celebrations.
"I'm speechless at what I'm watching," said former British number one Annabel Croft on BBC Radio 5 Live Sports Extra. "I've never seen anything like this."
The already fervent atmosphere went up another notch at the changeover. Fans sang loudly in a Davis Cup-style noise as they savoured every moment with the 11pm curfew looming.
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Djokovic saved a set point to force the tie-break, which was a fitting end to a compelling set.
But Nadal started the breaker with a double fault and then inexplicably patted a volley long at 4-4.
That handed the initiative to Djokovic who, with two serves for the set, whacked down an ace and chased down a drop-shot.
"I had the big chance with set point at 6-5 on his second serve. That's it. Anything could happen in that moment," said Nadal, who had won all 13 of his previous French Open semi-finals.
"Then I make a double-fault and missed an easy volley in the tie-break.
"These kind of mistakes can happen. But if you want to win, you can't make these mistakes."
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'We both wanted the fans to stay'
After the first semi-final between Tsitsipas and Alexander Zverev lasted over three-and-a-half hours, there was always a danger that the second match would go past the 11pm curfew.
Djokovic and Nadal did not start play until 7:10pm and, after the opening two sets each lasted an hour, the expectation was the match would be stopped for the crowd to be sent home.
Once Djokovic clinched the epic third set after 93 minutes, it seemed a logical point to clear the stadium. Then came another twist.
Boos initially greeted a stadium announcement – until the fans realised it was telling them they were allowed to stay and the jeers turned to cheers.
"Considering what we were living through in this match before the announcement, I think both of us wanted the crowd to stay," Djokovic told Eurosport.
"We both had tremendous support. These are the kind of matches we continue to play tennis for."
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