Novak Djokovic's quest for the first men's singles calendar-year Grand Slam in 52 years reaches its penultimate hurdle Friday in a US Open semi-final showdown with Tokyo Olympic champion Alexander Zverev.
It was German fourth seed Zverev who ended top-ranked Djokovic's bid for Olympic gold with a fightback July semi-final triumph in Japan and both men are girding for an epic rematch at Arthur Ashe Stadium as history looms.
"You have to be perfect, otherwise you will not win," Zverev said. "Most of the time you can't be perfect. That's why most of the time people lose to him."
Djokovic is expecting Zverev's best.
"I know it's going to be battle," Djokovic said. "But I'm ready for it. These are the hurdles I need to overcome in order to get to the desired destination."
Djokovic is trying to be the first man to sweep the major crowns in the same year since Rod Laver in 1969.
The 34-year-old Serbian seeks his fourth US Open title and 21st career Slam trophy, which would give him the men's record total he currently shares with Rafael Nadal and Roger Federer, both absent due to injuries, outright.
"I'm aware of the history. Of course it gives me motivation," Djokovic said.
"If I start to think about it too much, it burdens me mentally. I want to really go back to the basics and what really works for me mentally.
"I'm in a position that's very unique. I'm very grateful for that. I'm inspired to play my best tennis.
"I know a lot of people want to hear me talking about it. But let's talk about it hopefully on Sunday."
That is when Djokovic hopes to be playing for the Grand Slam against the winner of Friday's other semi-final between Russian second seed Daniil Medvedev and Canadian 12th seed Felix Auger-Aliassime.
Djokovic is 6-3 against Zverev, but the Olympic defeat stings.
"Tough ending for me emotionally," he said.
Zverev is on a 16-match win streak while Djokovic has won 26 straight Slam matches.
"I know his game very well," Djokovic said. "He has been playing very well. When we face each other, there's nerves, a lot of things on the line. It could go both ways. I think very few points will really determine the winner."
Zverev, last year's US Open runner-up, needs to get past Djokovic to have a chance at his first Grand Slam title.
"Against him, you have to win the match yourself," Zverev said. "You have to be the one that's dominating the points. You have to do it with very little unforced errors. He's the best player in the world. He's very difficult to beat."
Djokovic played what he called his best three sets at the Open to rally past Italy's Matteo Berrettini in the quarter-finals.
"I just went to a different level and I stayed there 'til the last point," Djokovic said. "That's something that definitely encourages me and gives me a lot of confidence prior to semi-finals."
Berrettini, who also lost to Djokovic in the Wimbledon final, marvels at that.
"He has this ability -- and probably that's why he's the best ever -- just to step up his game, his level, all the time," Berrettini said. "He starts to return better, to serve better. Doesn't matter how well I play, he just plays better."
Djokovic is ready for a marathon fight with Zverev.
"He's in a fantastic form. Next to Medvedev best form," Djokovic said. "Physically I feel as fit as anybody out there. So I can go the distance.
"I'm going to be ready to go five sets, five hours, whatever it takes. That's why I'm here."
Auger-Aliassime will play in his first Slam semi-final when he meets Medvedev.
"I need to step up and be confident," the Canadian said. "I need to try to put pressure on him. But it's going to be tough. I need to be ready for his best."
Medvedev, who lost to Djokovic in this year's Australian Open final, seeks his first Slam crown.
"I have this experience. I'm not going to be tight," he said. "If I play good, it's going to be not easy for my opponent."