Manila Mavericks player Serena Williams of the United States returns the ball against the Legendari Japan Warriors player Mirjana Lucic-Baroni of Germany during their women's singles match in the International Premier Tennis League in Pasay City, Philippines, on December 7, 2015.[Photo/Agencies]

Despite passing 34 in August, the Swiss reached the Wimbledon and US Open finals and handed Djokovic a rare defeat in the round-robin section at the World Tour Finals before the Serb took revenge in the title match.

The Swiss ended the year at three in the world and decided to skip four

straight Masters next season as he points his campaign towards the Rio Games and also saves more energy on Grand Slams.

Scot Andy Murray finished at two in a season where he led Britain to a first Davis Cup in 79 years.

While 14-time Grand Slam winner Rafael Nadal has been struggling all through the season but he believed he can come back on the right track.

"I always have the feeling that I am going to play better. I believe my level is to be there in the top eight. So even if I've had tough moments this year, I believe I can come back into the game," the Spaniard said.

In women's tennis, the case was similar as Williams also won three of the four Grand Slams in 2015, including the Australian and French Opens and Wimbledon.

Williams looked almost certain to become the first player since Steffi Graf in 1988, and just sixth player overall, to complete a calendar Grand Slam after reaching the semifinals of the US Open. With Flavia Pennetta then dumping out second seed Simona Halep in the first semifinal, the odds on the American landing an historic title shortened further.

Riding a 26-match win streak at Flushing Meadows, the world number one was overwhelmingly expected to sweep aside unseeded Roberta Vinci and set up a showdown with eventual champion Pennetta, against whom Williams owned a 7-0 career edge.

Instead her bid was crushed in stunning fashion as the 32-year-old Vinci rallied from a set down to claim a sensational 2-6, 6-4, 6-4 triumph, beating Williams for the first time to set up the first all-Italian women's Grand Slam final in the Open Era.

Despite the shock defeat at the US Open, Williams is the one that calls the shots in the entire season -- like always -- and her supremacy will be continuing next season.