Carlos Alcaraz and Novak Djokovic, who have played each other only once, will finally do so again on Friday in the French Open semifinals. Can the ultimate young talent beat the ultimate tennis mind?A moment arrives nearly every time a younger player seizes the advantage over Novak Djokovic, with designs of toppling him from his perch at the top of tennis.It doesn’t matter how deep a hole Djokovic has dug for himself, or how well the whippersnapper on the other side of the net might be playing.Maybe Djokovic is down by two sets, as he was against Stefanos Tsitsipas in the French Open final two years ago and against Jannik Sinner in the quarterfinals at Wimbledon last year. Perhaps Djokovic is hobbling around the court with an injury after letting his opponent draw even, as he was after four sets against Taylor Fritz at the Australian Open in 2021, when he had torn an abdominal muscle and coughed up a two-set lead.Then the other guy begins to think he might actually be on the verge of something grand, just as Carlos Alcaraz, the 20-year-old Spanish sensation, might do on Friday at the French Open in his semifinal showdown with Djokovic, a match the sport has been yearning for since the spring of 2022.The racket becomes a little heavier, the elbow a little tighter, as Djokovic’s foes start to imagine pulling off the win. After all these years, all these matches in the deep end of a Grand Slam tournament, Djokovic, 36, can spot it from a mile away.He doesn’t have to. Djokovic, a 22-time Grand Slam champion, is within 80 feet, and he believes in his heart that everything is about to go his way.It happened again on Tuesday after more than two hours of struggle against Karen Khachanov in the quarterfinals. Khachanov, the big, burly Russian with a hammer-like serve and forehand and nearly a decade less mileage on his legs, had taken the first set and forced a tiebreaker in the second. He had his opening.“He’s always there, you know, he’s always pushing,” said Karen Khachanov, who lost to Djokovic on Tuesday though he won the first set. “He always tries to find a way.”James Hill for The New York TimesOr not. A perfect, 7-0 tiebreaker drew Djokovic even. A break of serve in the first game of the next set put him ahead. Khachanov was finished.“The energy of the court shifted to my side,” Djokovic said after dispatching Khachanov.But when Djokovic faces Alcaraz, who has taken the No. 1 ranking from him twice in the past nine months, it will be a test against youth unlike anything Djokovic has faced before. The two have played only once, in May 2022, in Madrid; Djokovic and Alcaraz kept missing each other for one reason or another in the 13 months since.“A complete player,” Lorenzo Musetti, 21, of Italy, an Alcaraz victim this week in the fourth round, said of the player he came to know on Europe’s junior circuit.Singular moments when one generation takes over from another can feel like the shifting of tectonic plates. Every so often, men’s tennis delivers a torch-passing match: Pete Sampras tearing through John McEnroe at the 1990 U.S. Open; Roger Federer beating Sampras on Centre Court at Wimbledon in 2001. Is another one at hand?Daniil Medvedev, the world’s second-ranked player, and the only player currently in his 20s to beat Djokovic in a Grand Slam final, said not long ago that it is nearly impossible to beat Djokovic until you have first lost to him several times. Opponents need to get used to his shot patterns and his relentless ability to make them hit one more ball after they think they have ended the point.Not so for Alcaraz. Alcaraz beat Djokovic in their lone meeting, in a deciding-set tiebreaker no less (albeit in a best-of-three-sets match). So far Alcaraz has exhibited none of the fragility displayed against Djokovic in big moments by his contemporaries, or even the players a few years older than he is who were supposed to be the next generation of tennis stars.“I really want to play that match,” Alcaraz said late Tuesday after he blasted through Tsitsipas in the quarterfinals to lock in the showdown with Djokovic. “I’m going to enjoy it.”Maybe.One of the age-old adages about sports in general and tennis in particular is that by the time athletes have gained the wisdom and experience necessary to truly crack their sport’s code, their bodies have betrayed them. Djokovic has been giving this idea a run for its money.That is not accidental. He almost never drinks alcohol. He tries to sleep eight and a half hours a night, with a focus on his prime R.E.M. sleep hours. His postmatch gym and stretching routine sometimes looks as hard as a normal person’s workout.It is also difficult to argue that there is a sounder, more developed brain in tennis. Djokovic long ago redrew the angles of the game, finding new shots to hit and new ways to win matches and titles, becoming the world’s top-ranked player in an era when Roger Federer, Rafael Nadal and Andy Murray were making that as hard as it had ever been. These days, he changes the pace and rhythm of points with ease, like a baseball pitcher mixing in fastballs, curveballs, sinkers and changeups in every at-bat. And then he uses a serve-and-volley like a player from the 1980s, just to make sure everyone knows he can do that, too.He has spent years trading notes on mental fortitude with superstar athletes in tennis and other sports — Boris Becker, Kobe Bryant, Zlatan Ibrahimovic, to name a few. He meditates. He knows how to focus when he needs to like no one else. He has played five tiebreakers in this tournament without making an unforced error.Approaching his 45th Grand Slam semifinal, Djokovic has become a master of the five-set format, its almost inevitable emotional dips and swings. He seems to spend the first set gathering information about his opponent. If he loses that set, as he did in the last two Wimbledon finals, or even the next one, no big deal. There’s still plenty of time.“He’s always there, you know, he’s always pushing,” Khachanov said. “He always tries to find a way.”Whether that will work against Alcaraz is Friday’s great mystery. Alcaraz has so far shown so many of the benefits of youth — speed, strength, power, the optimism of a player who has scarcely any bad days — and so few of the pitfalls. He plays with a kind of limitless joy and freedom that other players struggle to comprehend, in the same way they struggle to handle the velocity of his forehand and his unmatched improvisational shotmaking.“He is able to make any shots on the court,” said Juan Carlos Ferrero, Alcaraz’s coach.James Hill for The New York TimesJuan Carlos Ferrero, Alcaraz’s coach, said he has always wanted to surge a step ahead. When he was playing Futures tournaments, in the sport’s third tier, he believed he was ready for Challengers, the second tier; when he was playing Challengers, he believed he was ready for the main tour.“He is able to make any shots on the court,” Ferrero said. “If you ask him to go to the net in a match point, he is able to do it. Or if I ask to return and go to the net, he is able to do it and make the drop shot.”He can play long points or short ones. Whatever the moment calls for.After Tuesday night, Tsitsipas had lost to both Djokovic and Alcaraz on the court where the two will face off Friday. Like everyone else, Tsitsipas said he had sized up the match as a showdown between the game’s most advanced brain, a player who seeks to maneuver his opponent and control every shot, and the game’s purest and fastest of talents.“One has experience, the other one has legs and moves like Speedy Gonzales,” Tsitsipas said. “One can hit huge, super big shots; and the other one prefers precision, to apply pressure and make his opponent move as much as possible.”Who will win?“I root for the kids,” Tsitsipas said.Against Djokovic, they need all the help they can get. More