American Sam Querrey knocked out the world no. 2 Novak Djokovic 0-6, 7-6, 6-4 in the second round of the Paris Masters.

The Serbian looked comfortably poised after winning the first set comprehensively. Querrey, however, made a great comeback in the next two sets. Djokovic was leading 2-0 in the second set but Querrey decided to turn things around and displayed some aggressive play to restrict the Serbian. His powerful serve and forehand proved too good for the seemingly exhausted world no. 2.

Djokovic will replace Roger Federer from Switzerland as the world number one when the rankings are released next Monday.

Djokovic was down with a stomach bug last week. He attributed his loss to poor fitness levels as the game progressed. "Great tennis at the start but I knew that the main problem today will be the continuity of my energy," he said. Unfortunately, it wasn't to be after the second set.

"And during the second set I already felt that physically I'm down and I struggled every game."

According to a Serbian newspaper, Djokovic had initially considered withdrawing from the Bercy tournament since his father Srdjan had been reportedly hospitalized with respiratory problems.

"I'd rather not talk about it," Djokovic added. "Sorry about that, but it's just private and I'd like to keep it that way. Some things happened and a lot of things are on my mind..., so right now I just need a couple of days' rest before (next week's season-ending ATP World Tour Finals in) London."

Earlier in the game, Querrey appeared to be struggling in the first set and was trying hard to avoid an embarrassing defeat.

Querrey told in a courtside interview: "It's my biggest, this win feels great. I served great. When I was down 6-0, 2-0 I just wanted to get a game and when I won that game I got a bit more confidence."

Querrey will next face the 14th seed Milos Raonic.

Meanwhile, Andy Murray, the third seed from Britain beat the French wildcard Paul-Henri Mathieu 7-5 6-3. "There were not too many rallies at the beginning," Murray said of the match. "At the end of the first set it was a bit better, with more rallies, but it was a tricky match."

Earlier South African Kevin Anderson defeated France's Richard Gasquet 7-6, 4-6, 6-1 with the French losing his opportunity to qualify for the ATP World Tour Finals in London.

Serbian Janko Tipsarevic defeated Igor Sijsling from Holland 6-4 7-6, while fourth seed David Ferrer cruised past Spaniard Marcel Granollers 6-1 6-3. He will now take on 16th seed Stanislas Wawrinka of Switzerland in the third round.

11th seeded Nicolas Almagro from Spain will face sixth seed Jo-Wilfried Tsonga of France after he beat compatriot Albert Ramos in three sets.

Michael Llodra, the local favorite defeated the 10th seeded John Isner 6-4 7-6, with it also ending the big-serving American's hopes of qualifying for London.