Rafael Nadal secured the year-end World No.1 ranking with a 7-5, 6-3 second-round victory over South Korean Hyeon Chung at the Paris Masters on Wednesday.
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.
Chung’s inexperience showed at the vital moment, as he threw away his serve to hand Nadal the first set after an hour of play.
Any thoughts of a quick end to the match were set to one side when Chung staved off four break points early in the second set.
The world number 55 has enjoyed a breakthrough season in 2017 and will play at the inaugural Next-Gen Finals in Milan later this month, but his resistance was finally ended in the French capital as Nadal broke to move within a service hold of victory.
And he closed it out with the minimum of fuss to add another piece of history to his illustrious career.
Earlier on Wednesday, fourth seed Alexander Zverev was dumped out by Dutchman Robin Haase in a 3-6, 6-2, 6-2 second-round defeat.
The 20-year-old German lost his composure after easing through the first set, as his bid for a third Masters title of the season was abruptly ended.
It was the world number 43 Haase’s first-ever win over a top-five player.
Home hope Lucas Pouille kept his slim hopes of qualifying for the World Tour Finals alive by seeing off Spaniard Feliciano Lopez 6-3, 6-4, but US Open runner-up Kevin Anderson’s chances ended with a 5-7, 6-4, 7-5 loss to Fernando Verdasco.
Rafael Nadal survived a rollercoaster encounter with fourth seed Marin Cilic to power into Sunday’s final of the Shanghai Masters and a possible showdown with old rival Roger Federer.
The Spanish world number one, who has never won the tournament but is on a terrific run of form, finally saw off the Croat after saving three set points in the opener on the way to a tense 7-5, 7-6 (7/3) victory.
Number two Federer plays Juan Martin del Potro in the other semi-final later Saturday after the Argentine said he was fit despite hurting his wrist in a fall in the quarter-finals.
Cilic had only ever got the better of 16-time Grand Slam winner Nadal once in five previous meetings, but he made him work hard for this latest win.
Nadal, pursuing a seventh title this season, put Cilic under immediate pressure in the Croat’s first two service games.
But the 29-year-old Cilic, the 2014 US Open champion, eventually settled, only to squander three set points as Nadal hung on grimly.
In the next game the 31-year-old Nadal capitalised, breaking Cilic on the way to claiming the first set.
With the crowd firmly in his favour, the Spaniard broke Cilic again in the third game of the second set, only for Cilic to break back for 3-3 when Nadal put his simple volley into the net.
An angry Nadal bashed his racquet twice on his knee.
They exchanged a further break apiece to race into the tie break, before a grateful Nadal pulled away at the last.
— Tennis TV (@TennisTV) October 14, 2017
The 31-year-old Spaniard was never really in trouble against the temperamental Australian in a 6-2, 6-1 rout in 92 minutes on Beijing’s outside hard courts.
Nadal, a 16-time Grand Slam winner, came to the Chinese capital on the back of winning his third US Open.
He saved two match points in his nervy opener against Frenchman Lucas Pouille.
But after that Nadal sliced through the opposition to win the China Open for the first time since making his debut in Beijing in 2005.
Since then Nadal has gone on to become one of the greatest players of all time and he underlined his brilliance in swatting aside the 22-year-old Kyrgios.
The world-ranked 19 displayed his best side in forcing Nadal to 2-2 in the first set, but his other side emerged later.
Kyrgios was already on a warning from the umpire from the first game of the match for something he said.
And when he went down 30-0 on Nadal’s serve at 2-2, he began the first in a series of lengthy discussions with the umpire – frequently spreading his arms in despair.
The Australian, going for a fourth career title, shook his head and continued the discussion as he trudged back to his chair, initially to whistles from the crowd and then cheers to encourage him.
Kyrgios, whose undoubted talent has often been overshadowed by his on-court conduct, collected a penalty point as his title hopes quickly evaporated.