Carlos Alcaraz admitted tension got the better of him after he was hobbled by cramp in his hotly-anticipated French Open semi-final against Novak Djokovic.

The 20-year-old had just won an electrifying second set to level the contest and looked like he might be grabbing the ascendancy when, after hitting a return in the second game of the third, his whole body seized up.

Alcaraz managed to carry on but won only one more game as Djokovic triumphed 6-3 5-7 6-1 6-1 to reach a 34th grand slam final, where he will face Casper Ruud.

The Spaniard did look a lot more anxious than usual at the start of the biggest match in men’s tennis for a year and, asked what had caused the cramp, he said: “The tension of the match.

“I started the match really nervous. The tension of the first set, the second set, it was a really intense two sets, as well. I have never felt something like I did today. I have never felt that tension that I did in that match.

“I disappointed myself, and in a match like this, coming to this match with great feeling, feeling great physically, and cramping at the end of the second set, beginning of the third set. It was really disappointing.”

This was only the second time Djokovic and Alcaraz had played each other and the first at a slam, with the young Spaniard having prevailed in Madrid last year.

The 16-year age gap was the biggest in any Roland Garros semi-final in the open era and it seemed a pivotal match in the generational battle going on in men’s tennis as well as for Djokovic’s hopes of pulling away from his rivals at the top of the all-time lists.

“It’s not easy to play against Novak,” said Alcaraz, who won a series of long matches to claim his first grand slam title at the US Open last year, where Djokovic was absent because of his vaccination status.

“If someone says that he gets into the court with no nerves playing against Novak, he lies.

“Of course, playing a semi-final of a grand slam, you have a lot of nerves, but even more with facing Novak. Next time that I’m going to face Novak, I hope to be different, but the nerves will be there.”

Djokovic was the better player in the first set but the second was a tremendous contest, with Alcaraz showcasing his spectacular brand of tennis, not least a stunning winner in the third game when he chased back towards his own baseline and somehow flicked the ball inside the sideline on the turn.

Djokovic was the first to call the trainer for treatment to his right forearm and Alcaraz broke for 5-3 before holding three set points two games later, but each time his opponent fought back.

Alcaraz did finally take his fourth set point on Djokovic’s serve at 5-6 but several minutes later the match was effectively over.

The Spaniard had to forfeit a game to have treatment, drawing loud and prolonged boos from the crowd when they realised what had happened, but that was the least of his worries.

He could barely move during the rest of the third set and, although he rallied at the beginning of the fourth, it was nowhere near enough to turn it back into a contest.

“I started to cramp in my arm,” explained Alcaraz. “At the beginning of the third set I started to cramp in every part of my body, not only the legs.”

Asked if he considered not finishing the match, the 20-year-old said: “I would have felt sorry about myself if I would retire. I’m in a semi-final of a grand slam. I thought that probably I have one per cent chance to come back.”

Djokovic, who has not lost a slam match for more than a year, will now be an overwhelming favourite to become the first man to win 23 grand slam singles titles in the final on Sunday.

He had sympathy for his opponent, saying: “First and foremost I have to say tough luck for Carlos. At this level, the last thing you want is cramps. I feel for him, I feel sorry and hope he can recover and come back very soon.

“I told him at the net, he knows how young he is. He’s going to win this tournament I’m sure many, many times. He’s an unbelievable player.

“It’s tough obviously for him to not know whether he should finish the match but congratulations to him for the fighting spirit.

“Towards the end of the second set I wasn’t feeling fresh at all. We went toe to toe and then this thing happened. I just tried to stay focused. I saw that he’s struggling but I didn’t want to think too much what’s going on on the other side of the net.

“I’m incredibly proud to reach another final.”

Not for the first time this fortnight, Djokovic was booed on several occasions throughout the match, including when he celebrated winning points in the fourth set.

“I don’t mind,” he said with a wry smile. “It’s not the first (time), probably not the last. I’ll just keep winning.”

Ruud reached the final for the second year in a row, hammering Alexander Zverev 6-3 6-4 6-0.

The Norwegian fourth seed struggled at the beginning of the season but has found top form again at Roland Garros and will try to win a first slam title at the third time of asking having lost here to Rafael Nadal 12 months ago and to Alcaraz in New York.

“I just went out there and tried to play without too many feelings, without thinking too much,” he said.

“Today I just played really well and, from the beginning to the last point, everything was sort of going my way. I’m just very happy to win this match. Hopefully third time can be the charm for me.”