World number one Novak Djokovic of Serbia poses with the trophy after beating Britain's Andy Murray in their men's singles final tennis match at the Paris Masters tennis tournament November 8, 2015.[Photo/Agencies]

BEIJING -- World number ones Novak Djokovic and Serena Williams proved they are still in a class of their own in tennis world, winning six of eight Grand Slam titles in 2015.

Djokovic collected 11 titles and 82 wins which brought him three of the four majors -- the Australian and US Opens and Wimbledon.

"It's the best year of my life, no question about it," the 28-year-old Serb said during this season's Shanghai Masters. "Everything is working great. I'm very grateful for the opportunity to be able to play this well, to be successful. I don't want to get carried away by success because I want to be playing on this level for many more years to come."

Asked about his secret to success, Djokovic said it's all about self-discipline.

"I take care of my body. I respect the preparation and recovery routines that I have with my team. It's all about self-discipline and being able to understand what you need to do to have the kind of longevity and to endure throughout the entire year, to be able to play this many matches on a high level."

"I know that one of the things that you have to do in order to keep playing on a high level is stay committed and stay determined to this lifestyle that is not easy, traveling all the time. Now that I'm a father, that makes it a little bit more difficult. I have the support of the close ones, my wife, the most important one, and my brothers, my team. Everybody is behind me on the quest of being the best I can be," added the Serb, who now has 10 Grand Slam titles.

Djokovic also swept away six of the nine Masters and made it perfect with a fourth successive season-ending World Tour Finals triumph in London.

Djokovic reached the final of every tournament he played with the exception in Doha where Ivo Karlovic stunned him in the quarterfinals.

From then on it was one-way traffic -- indoors, outdoors, hardcourt, clay and grass -- the Australian Open, Masters in Indian Wells, Miami, Monte Carlo and Rome and then Wimbledon, US Open, Beijing, the Shanghai and Paris Masters and London.

But unfortunately, Djokovic lost to Swiss Stan Wawrinka at Roland Garros final, which left him still seeking a first French Open and a career Grand Slam title.

Roger Federer, who hasn't added to his 17 majors since 2012 Wimbledon, continued to play his top game.