Russia's Daniil Medvedev became the 27th player to reach the number one spot in the men's ATP tennis rankings on Monday.
Medvedev overtakes 20-time Grand Slam champion Novak Djokovic of Serbia, who had held the top spot for a record 361 weeks in total.
Medvedev, the 2021 US Open champion, becomes the first player outside the Big Four of Djokovic, Roger Federer, Rafael Nadal and Andy Murray to move to number one in the world rankings for 18 years, three weeks and six days - since Andy Roddick reached top spot on 1st February 2004.
The last time there was a new world number one in men's tennis was more than five years ago, when Murray made it there on 7th November 2016.
Medvedev is the third Russian to achieve the feat, and joins Yevgeny Kafelnikov and Marat Safin who were respectively top for six and nine weeks.