Djokovic fell to a 6-4 7-6 (7-4) defeat at the hands of 123rd-ranked Jiri Vesely, who now holds a 2-0 record against the 34-year-old.

Medvedev will become the first new world No 1 other than Djokovic, Roger Federer, Rafael Nadal or Andy Murray since February 1, 2004.

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The Serbian athlete had occupied the world No 1 spot since overtaking Rafael Nadal on February 2, 2020, setting a new record last March for weeks at the top which currently stands at 361.

"Unfortunately, it wasn't my day," Djokovic told reporters. "I congratulate Jiri. He played better. He just went for his shots. His serve was big. His whole game was big. I expected myself to play on a higher level, for sure. I mean, I can do better. But credit to Jiri.

"The more matches I play, the more confident I will be, the more comfortable I'll be feeling on the court."

'Great to have a new world No 1'

Djokovic had known going into the Dubai Championships that he could lose his world-leading status if Medvedev won the ATP 500 in Mexico. Medvedev entered the competition in Acapulco as the top seed and will now take to court for the quarter-finals knowing that he will be now top of the rankings on Monday morning.

Vesely is one of just three players to have defeated Djokovic multiple times and never lost to him - the others being Nick Kyrgios and Marat Safin. The 28-year-old is the lowest-ranked player to beat Djokovic for almost four years.

"I never really thought I would have a chance against Novak," Vesely said. "He is one of the greatest of all time. It is great for tennis to have someone new at world No 1. Novak is such a champion, he has been No. 1 for 361 weeks, but tennis needs new world No 1s and there is a new generation coming up and I think it is great."

Speaking at the weekend, Djokovic said: "He deserves to be number one. Eventually it's going to happen. If it happens this week, I'll be the first one to congratulate him."