PARIS (AP) — Five months after his first French Open title and completing a career Grand Slam in Paris, Novak Djokovic's reign over men's tennis could be about to end in the City of Lights.

Djokovic, a three-time defending champion, lost in the Paris Masters quarterfinals on Friday, leaving his No. 1 ranking open to being snatched by Andy Murray.

The British player can rise from No. 2 to 1 in the ATP list for the first time if he reaches the final. He needs one more win after beating Tomas Berdych 7-6 (9), 7-5. His semifinal opponent will be No. 5 Milos Raonic, who defeated Jo-Wilfried Tsonga 6-2, 7-6 (4).

Murray was aware of Djokovic's defeat when he took the court and was sometimes hesitant against Berdych. He rallied from 6-1 down in the tiebreak, and needed four match points to overcome the Czech.

"Before the match there were a few more nerves maybe than there was earlier in the week," Murray said. "But once I got out there, I didn't feel any different to any other match. I didn't play the match differently to how I would have played other matches, which is good. Tomorrow will probably be the same, probably."

So dominant on the Parisian red clay last June, Djokovic was far from his best on super-fast carpet and was beaten by Marin Cilic 6-4, 7-6 (2), his first loss against the former U.S. Open champion in 15 matchups.

Djokovic made uncharacteristic mistakes from the baseline, called the tournament doctor during the first set, struggled on his serve, and destroyed his hopes of a comeback when he served for the second set at 5-4, hit two double faults, and was broken.

He fought until the end though, saving two match points in the 12th game with a fine backhand volley and crosscourt forehand winner, the rare moments when he looked like his usual self. But Cilic, who struck nine aces overall, served extremely well to prevail in the tiebreaker and end Djokovic's 17-match winning streak in Paris.

"I wasn't on the level that I could have been on," Djokovic said. "I was also, in this kind of circumstances and with this level of play, in a good position to take the match into the third set, and then two double faults. Just in important moments I wasn't able to deliver. He is a deserved winner."

Djokovic has held the top spot for 122 consecutive weeks. But after winning the French Open for the first time in June, his form has yo-yoed. He lost in the third round at Wimbledon, and in the first round of the Olympics. At the U.S Open, he won the first set in the final but Stan Wawrinka rallied to beat him.

He admitted his long-awaited victory at Roland Garros took a toll.

"There was pride and satisfaction in the success I have had with my team, but in the other hand, it was also very exhausting," he said. "At a certain point, I had to reach this kind of phase where I had to reflect and say, 'OK, I have played on the highest possible level for that much.' The drop of form is normal in sports. I'm not too concerned about how the future will go for me."

If he makes the final, Murray, who has spent 76 weeks at No. 2, will become the 26th player to reach No. 1 since the rankings started in 1973.

"He's definitely a player who deserves that," Djokovic said. "Undoubtedly, much respect for what he has done. We have known each other since very, very early days. We were, I think, 11 years old when we first played against each other. And to see how he has raised his level in the last 12 months is quite extraordinary."

Murray could become the oldest first-time No. 1 at 29 since John Newcombe made it at 30 in 1974.

"Getting to No. 1, like I said, is 12 months of work, basically," Murray said. "Consistency. I have never done that before. My career, I have had periods where I have been consistent for a few months at a time and then dropoffs. I have put myself in a position to do something that takes a lot of consistency, a lot of concentration for a long period of time. I'm happy about that."

Cilic, who qualified for the ATP Finals this week, will take on American John Isner in the semifinals.

"The end of the season is just getting better and better," Cilic said.

Isner won a hard-fought all-American contest against Jack Sock 7-6 (6), 4-6, 6-4.

Tsonga's loss combined with Berdych's exit played in favor of Dominic Thiem, who qualified for the ATP Finals in London for the first time. Thiem completed the elite field of Djokovic, Murray, Wawrinka, Raonic, Kei Nishikori, Gael Monfils and Cilic.