Andy Murray marked reaching the number 1 spot by beating John Isner to win his eight ATP tour title of 2016, by claiming the Paris Masters.
The Briton was playing in his 12th final of an impressive year and beat the American tennis player 6-3 6-7 6-4.
It was the Scot’s fourth title in succession after wins in Beijing, Shanghai and Vienna and his 14th career Masters 1000 triumph.
The ranking changes are made official on Monday and will make the Scot the first British singles player to hold the top spot since the ATP Tour points system was introduced in 1973.
“This has been an incredible journey for me to get to the top of the rankings,” said Murray, who will move 405 points above long-time rival Novak Djokovic.
He now heads to the season-ending World Tour Finals as top seed for the first time – but if previous number one Novak Djokovic wins every match at the Finals he will reclaim the top ranking he held for 122 weeks.