Rafael Nadal secured the year-end world number one ranking with a 7-5, 6-3 second-round victory over South Korean Hyeon Chung at the Paris Masters today.
The 16-time Grand Slam champion is the oldest man to finish a season at the top of the rankings at the age of 31, after a year that saw him win the French and US Opens.
It is the fourth time the Spaniard has achieved the feat after 2008, 2010 and 2013.
Nadal went into the match knowing victory would give him an unassailable lead as world number one over old rival Roger Federer, after the Swiss legend withdrew before the start of the tournament.
The 21-year-old
Chung put up a brave fight at the Bercy Arena, but a fired-up Nadal proved too hot to handle.
Nadal will next face Pablo Cuevas in the last 16, after the unseeded Uruguayan edged out Albert Ramos-Vinolas 6-7 (5/7), 7-6 (7/1), 6-2.
Chung sent out an early warning of his intent with a ripping forehand winner to break Nadal in the third game.
The top seed responded, though, taking the next four games to open up a 5-2 advantage.
Nadal was broken when serving for the set as Chung hit back, but the turning point came as the world number one saved a break point in game 11, marked with a trademark fist-pump.