The 2015 tennis season is officially over with Novak Djokovic capping off his amazing season with victory against Roger Federer 6-3 6-4 at the ATP World Tour Finals in London. The Serb clinched his fourth consecutive trophy in men’s tennis season-finale tournament at the O2 Arena in the championship match.Djokovic previously lost to Federer in the group stages at The O2 7-5 6-2, but the top seed Serb beat the Swiss in a repeat of the 2014 finals on Sunday to win his 11th title of the season and retain his ATP crown. Their career head-to-head record is now leveled at 22-22. However, Djokovic still stands heavily with the Serb leading Federer 11-6 in final clashes.The World No. 1 Serb couldn’t be happier with a great 2015.“I’m obviously very proud to have these achievements with my team,” Djokovic said in an interview as quoted on men’s tennis official website. “It’s been a long season, but the best of my life.” Djokovic ended the season with 82-6 win-loss record.Meanwhile, six-time titlist Federer will finish the season as World No. 1 Swiss and No. 3 in the Emirates ATP World Rankings. He won six titles from his 11 final appearances at the Brisbane International, Dubai Duty Free Tennis Championships, Cincinnati Open, the inaugural Istanbul Open, Gerry Weber Open, and Swiss Indoors Basel. This season, Federer was also a runner-up for five times. All his five final losses came against Djokovic times at the BNP Paribas Open Indian Wells, Italian Open, Wimbledon, and the US Open.Going into the next season, Federer eyes the first grand slam of the year at the Australian Open following his second straight ATP World Tour Finals defeat after withdrawing last year due to an injury.“It starts with the Australian Open, which is just around the corner,” Federer said “That's what I see next. Then once Australia's over, that's when I look more towards the future.”Contact the writer at feedback@IBTimes.com.au, or let us know your thoughts below.