Rafael Nadal became the oldest year-end world number one since rankings began by beating Chung Hyeon 7-5 6-3 in the second round of the Paris Masters. It is all the more remarkable because Nadal was given to a lot good for the case he has just one year ago.
"I'm very, very happy for everything", he said on court following the victory over Chung.
Nadal is also the oldest, testimony to his relentless determination.
Roger Federer paved the way for his long-time rival to end 2017 top of the rankings after pulling out of the Paris Masters in order to rest ahead of the ATP Finals.
Nadal was not at his best against the 21-year-old Chung, but was rarely tested.
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.
Chung saved four break points in a long fourth game of the second set lasting 12 minutes, holding for 2-2.
The 31-year-old Nadal will be the oldest year-end number one and first season-ending number one over the age of 30 since the Emirates ATP Rankings were established in 1973. With no Federer here, the draw is relatively open for Nadal to make a real run at the title, which would bring him closer to a career sweep of Masters events (he also has never won Miami or Shanghai). He will next face Pablo Cuevas of Uruguay.
Fourth seed Alexander Zverev looked jaded in a surprise 3-6, 6-2, 6-2 loss to Dutchman Robin Haase in his opening match.
Haase next plays No. 13 Juan Martin del Potro, who eased past Joao Sousa of Portugal 6-2, 6-2. Who will win the World Tour Finals this year?
After saving three match points in the tiebreaker, Schwartzman leveled the match when Isner made a forehand error.
Pouille, the champion in Vienna last weekend, eased to a 6-3, 6-4 win over Feliciano Lopez while Isner, who would need to win the title in Paris to stand a chance, was a 7-6 (2), 6-7 (11), 6-3 victor over Diego Schwartzman.
Bulgarian world number eight Grigor Dimitrov, who has already booked his ticket for the Tour Finals, knocked out French favourite Richard Gasquet with a straightforward 6-4, 6-4 win.