Paris - Marin Cilic dumped a struggling Novak Djokovic out of the Paris Masters quarter-finals on Friday to pave the way for Andy Murray to become the new world No 1.
Cilic had lost all 14 previous meetings with Djokovic but cast the Serb's 122-week reign at the top of the rankings into serious doubt with a 6-4, 7-6 (7/2) victory.
Murray faces Tomas Berdych for a place in the semi-finals later and is just two wins from supplanting long-time rival Djokovic at the summit.
If the Briton defeats Berdych he would then take on Milos Raonic or Jo-Wilfried Tsonga for a chance to claim the No 1 ranking.
Record four-time champion Djokovic arrived in Paris needing to reach the final to ensure he remained ahead of a rapidly approaching Murray.
But the Serb's bid to register a fourth straight title in the French capital ended abruptly as an improbable escape act fizzled out against an in-form Cilic.
The ninth seed, who on Thursday qualified for the Tour finals in London, broke immediately to signal his intent against a player who had totally dominated him in his career.
In typical fashion Djokovic then hit back straight away to level, but Cilic's confidence was undimmed and the Croat capitalised on a shaky service game from his opponent at 5-4 to grab the opening set.
Former US Open champion Cilic threatened again early in the second, but Djokovic landed a crucial breakthrough at 4-all to serve for the set.
An undeterred Cilic broke back, though, and had the top seed on the ropes as two match points passed him by at 6-5 on the Djokovic serve.
However, there was to be no remarkable recovery this time for Djokovic, as Cilic took charge in the tie-break and closed out a famous win at the fourth attempt.
"It's good for me, I played great tennis. He had beat me 14 times but we had close matches and that helped me play better," Cilic told Sky Sports.
"I served really well today, hit the spots well, I didn't give him too many chances."
ISNER TRUMPS SOCK
American John Isner awaits Cilic in last four after he outlasted compatriot Jack Sock 7-6, (8/6), 4-6, 6-4.
Isner and Sock, who teamed up to win the doubles in Shanghai last month, traded crunching blows as the first set headed to a tie-break, but the latter was made to pay after failing to convert a set point.
Sock was playing his 33rd match - singles and doubles combined - in as many days and the American No 1 appeared to run out of steam as he dropped serve early in the second.
But the world No 24 rebounded by breaking Isner's serve for the first time this week and then repeated the trick once more to force a third set.
Isner raced 4-0 ahead in the decider, and although Sock fought gamely to claw to within a break, his rally fell short this time.
Berdych also has plenty at stake when he plays Murray with the 2005 Paris champion needing to win to stay in the race for the final London berth.
Results from the fifth day of the ATP Paris Masters on Friday (x denotes seeding):
Marin Cilic (CRO x9) bt Novak Djokovic (SRB x1) 6-4, 7-6 (7/2)
John Isner (USA) bt Jack Sock (USA) 7-6 (8/6), 4-6, 6-4