Having battled through 59 encounters with Rafael Nadal over 16 years of epic rivalry, Novak Djokovic faces the Spanish legend's heir apparent Carlos Alcaraz at the French Open in a match laced with era-defining potential.
Djokovic will be playing a 45th Grand Slam semi-final on Friday; for Alcaraz, it will be just his second.
With Roger Federer retired and Nadal nursing a hip injury until next year, 36-year-old Djokovic has the responsibility of preserving the legacy of the 'Big Three'.
"It's definitely the biggest challenge for me," said Djokovic, chasing a third French Open title and men's record 23rd Slam which would break the tie he currently shares with Nadal.
Friday's showpiece will be the first time Djokovic and Alcaraz have met at a Grand Slam and only the second time in their careers.
Alcaraz, then still 19, defeated the Serb from a set down in the semi-finals of the Madrid Open last year, a day after he had knocked out Nadal on the faster, higher altitude courts of the Spanish capital.
He predicted then that the "sky's the limit" and he wasn't far wrong, claiming a maiden Slam title at the US Open and becoming the youngest world number one.
"He carries himself very well. Brings a lot of intensity on the court. Reminds me of someone from his country that plays with a left hand," said Djokovic of a player who is 16 years his junior but already boasts the competitive DNA of Nadal.
Djokovic has 90 career wins at Roland Garros and is playing his 11th semi-final.
- 'Guy to beat' -
When he made his tournament debut in 2005, Alcaraz was just two but despite the age gap, Djokovic is keen to measure himself against the Spaniard for the first time at a major.
"If you want to be the best, you have to beat the best. He's definitely a guy to beat here. I'm looking forward to that," added Djokovic, bidding to reach a seventh final in the last eight majors in which he has played.
Alcaraz fell at the quarter-finals in Paris 12 months ago while Djokovic's run ended in the semi-finals at the hands of Nadal.
The Spaniard then lost in the last 16 at Wimbledon where Djokovic was crowned champion for a seventh time.
When Alacaraz swept to his maiden Slam in New York in September, the Serb was stranded at home, banned from entering the US because of his refusal to be vaccinated.
Hopes they would meet at the Australian Open, when Djokovic collected a 10th Melbourne title, were dashed when Alcaraz pulled out with a leg injury.
"Since the draw came out, everyone was expecting this semi-final against Novak, myself as well. Since last year I really wanted to play again against Novak," said Alcaraz.
"We are both playing a great level. It's his 45th semi-final of a Grand Slam; this is going be my second. I would say his experience is better, but I'm not going to think about that."
Greek world number five Stefanos Tsitsipas has had a close-up view of both men this year.
- 'Speedy Gonzalez' -
He lost to Djokovic in the Australian Open final and was swept out of Roland Garros by Alcaraz in straight sets in the quarter-final.
"Djokovic has experience; Alcaraz has legs and moves like Speedy Gonzalez," said Tsitsipas.
"Alcaraz can hit huge, super-big shots and Djokovic prefers control over anything else, probably control and precision, to apply pressure and just make the opponent move as much as possible."
There is also Djokovic's famous iron will -- in the five tiebreaks he has played in Paris this year, he hasn't committed a single unforced error.
The clash between Djokovic and Alcaraz has overshadowed Friday's other semi-final between 2022 runner-up Casper Ruud and Olympic champion Alexander Zverev who is in the last four for a third successive year.
Twelve months ago, Zverev suffered season-ending ankle ligament damage in his semi-final against Nadal.
"That was the most difficult year of my life," said the 26-year-old German.
"I love playing tennis and the sport and competition were taken away from me."
Zverev leads Ruud 2-1 in their head-to-head match-ups but they have never met on clay.
That could prove significant as world number four Ruud boasts the best record on the surface since 2020 with 86 wins.