Novak Djokovic has been dethroned by Daniil Medvedev as the world number one male tennis player after suffering a shock defeat to Jiri Vesely at the Dubai Open, where the Serb superstar was playing for the first time since he was deported from Melbourne following his failed bid to play at the Australian Open.
Medvedev's progress to the quarterfinals of the Mexican Open, where he is expected to beat world number 103 Yoshihito Nishioka next, means he became officially the best tennis player in the world without even playing as a result of a change in the ranking points caused by Djokovic's loss.
World number 123 Vesely's 6-4, 7-6 win over Djokovic marked an abrupt end to a promising early campaign for the 20-time Grand Slam champion in his first tournament of the year.
The icon had not dropped a set in his first two matches, easing past 2020 Olympic Games silver medalist Karen Khachanov in the round of 16.
Former Dubai champion Djokovic's return to the tournament had been much-anticipated after his agony in Australia, where he was grilled by border force officials, detained in a hotel and ousted before the first Grand Slam of the year began following the second of two court hearings as the country's government ultimately succeeded in canceling his visa.
Unvaccinated Djokovic had flown to Australia on the understanding that he would be allowed an exemption to enter the country and compete because he had recovered from Covid in December.
The 34-year-old has said he is not against Covid shots but will remain unvaccinated for the time being.
Players were not required to have taken vaccines to enter Dubai and play in the ATP 500 event, although there have been widespread reports that Djokovic may face greater difficulties in entering events with tighter restrictions later in the year, and the star has admitted he would be willing to consider foregoing tournaments in order to remain unvaccinated.
Vesely, who beat Djokovic on the only previous occasion when they have met each other, served for the match at 5-3 in the second set, only for his opponent to break back in a response that some viewers believed would signal a conclusive comeback.
The man who has never gone past the fourth round of a Grand Slam then won the crucial tie-break 7-4 in a victory that knocked Djokovic off the top of the rankings for the first time since January 2020.
Medvedev is yet to lose a set in Acapulco and could face a showdown with Rafael Nadal, who he lost the Australian Open final to in a five-set thriller.
Nadal has made his best ever start to a season, winning his 12th successive match with a 6-0, 6-3 victory over Stefan Kozlov that lasted just 47 minutes.
He could meet Medvedev in the semifinals of the tournament, which continues until Saturday.