(CNN) -- Novak Djokovic walked on to the court in a Darth Vader mask -- but it was the world No. 1 elect who was spooked after crashing out of the Paris Masters in his opening match.
The Serbian tennis star, who is known for his pre-match antics, suffered a Halloween horror show as he lost 0-6 7-6 (7-5) 6-4 to Sam Querrey in the second-round clash.
The U.S. player, ranked 23rd, hit 18 aces on his way to grinding out victory in two hours, meaning Andy Murray is the highest-ranked player left in a field weakened by the absence of current No. 1 Roger Federer and Rafael Nadal.
Murray secured his place in the next round following a comfortable 7-5 6-3 win over Paul-Henri Mathieu of France and will now face Poland's Jerzy Janowicz.
At least Djokovic will now have a sufficient recovery period ahead of the World Tour Finals, which begin in London on Monday -- when he officially returns to the top of the rankings due to Federer's decision not to defend his Paris title.
"I knew the main problems would be my energy, it wasn't there during the second set. I really felt my level drop," Djokovic said.
"I struggled every game, but on the brighter side I have time to rest. I've been through a really difficult period this last few weeks. There have been a lot of things on my mind, some things happened.
"I have a couple of days now to rest. I've had to face some things a bit unusual for me, but when you lose a match you move on and go to the last tournament of the year."
Querrey, who will next play either Canadian 14th seed Milos Raonic or Frenchman Jeremy Chardy, was relieved to recover after losing the first eight games of the match.
"It was a little embarrassing. I walked over to my girlfriend and my chiropractor and I said, 'I hope I can get two games in this set.'
"Once I got the two games I kind of settled down. I was like, 'Okay, that's all I want.' But then I got rolling and got more confidence and started serving better and being a little more aggressive."
While Djokovic is assured of his place in the eight-man London line-up, his compatriot Janko Tipsarevic is still fighting to earn one of the remaining two berths at the season finale.
Tipsarevic defeated Dutchman Igor Sijsling 6-4 7-6 (7-0) to ensure his passage to the third round, where he will face Argentine ninth seed Juan Monaco -- who can potentially qualify if he reaches the final, depending on other players' results.
However, Richard Gasquet's hopes of making it to London ended when the the French 12th seed lost to big-serving South African Kevin Anderson in three sets.
Elsewhere, Juan Martin Del Potro eased past Colombia's Alejandro Falla 6-2 6-2 to set up a third round clash with France's Michael Llodra.
Llodra ovecame 10th seed John Isner 6-4 7-6 (7-5) to end the American's hopes of making it through to London.
Nicolas Almagro will take on Jo-Wilfried Tsonga in the third round after he overcame fellow Spaniard Albert Ramos 7-6 (7-1) 6-7 (4-7) 6-3.
France's Gilles Simon will face Japan's Kei Nishikori following a straight forward 7-5 6-3 win over Victor Hanescu.