New York, Sep 11 : Germany's Alexander Zverev said after his loss to Novak Djokovic in a five-setter at the US Open semifinal on Saturday (IST) that the Serbian was not world No. 1 without a reason, adding that "he comes up with the best tennis when he needs to". Djokovic, the winner of 20 majors, won 4-6, 6-2, 6-4, 4-6, 6-2 after three hours and 38 minutes to set up a title clash with Russia's world No. 2 Daniil Medvedev. "It was a great battle. Kind of a little bit disappointed with the start of the fifth set. To be honest, apart from that, it was a good match. I think we both left it all out there," Zverev said. "The second break in the fifth set was so ridiculously unlucky that it sometimes happen. But he's No. 1 in the world for a reason and he showed that tonight," the German told atptour.com. Having foiled the Serbian's bid for the Golden Slam in 2021 with his victory from a set and a break down in the Tokyo Olympics semifinal, the German was confident he could repeat the feat at Flushing Meadows. Following his run to the gold medal and victory in Cincinnati, Zverev was on a 16-match winning streak to the semifinals. He had dropped only one set en route this campaign -- in the third round against Jack Sock -- and came within a set of becoming the first man since Djokovic in 2015/16 to reach consecutive US Open finals. Zverev admitted the edge his opponent held in the semifinal came down to his mental toughness on the biggest points. "He comes up with the best tennis when he needs to. We play 55-shot rallies. The only way for me to win that rally is to hit a forehand winner. That says it all, on a set point ," Zverev said. "There is a reason why he's won 20 Grand Slams. There's a reason why he's spent the most weeks at World No. 1. There's a lot of reasons for that. I think mentally he's the best player to ever play the game. Mentally in the most important moments I would rather play against anybody else but him." The 24-year-old expected his conqueror to complete the Grand Slam in Sunday's final against second seed Daniil Medvedev. "Nobody thought anybody will do it again, what Rod Laver did. To see him have the chance on Sunday -- I do believe that he will do it -- is great. He's breaking every single record that there is," Zverev said. "If you look at the stats, if you look at the pure game of tennis action, he's the greatest of all time. Nobody is there with him, because most weeks World No. 1, most ATP Masters 1000 titles, most likely going to be the most Grand Slams at the end of the day. And he has the chance of winning all four in the same year. How do you compete with that?" /IANS