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 number one.

Cilic had lost all 14 previous meetings with Djokovic but cast the Serb's 122-week reign at the top of 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 number one ranking.

"If he gets it, which he is in a very good position to do that, he's definitely a player who deserves that," said Djokovic.

The record four-time champion 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.

"Credit to Marin and congratulations. He definitely played better today, and he deserved to win," said 29-year-old Djokovic.

"I wasn't on the level that I could have been on. Obviously, there are things I could have done better. And just in important moments I wasn't able to deliver."

Ninth seed Cilic, 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.

Isner into semis

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.

The top seed uncharacteristically gifted the break back, though, after a pair of costly double faults, and Cilic had him on the ropes as two match points passed by at 6-5 on a faltering Djokovic serve.

There was to be no remarkable recovery either 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."

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 number one appeared to run out of steam as he dropped serve early in the second.

But the world number 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.