That Novak Djokovic already has sewn up the world's No. 1 ranking hardly seems to matter now.

Tennis.com reported that the ATP World Tour Finals got the title match everyone seemed to want: No. 1 Novak Djokovic vs. No. 2 Roger Federer. With Rafael Nadal sidelined with injury, Djokovic and Federer arguably have become the biggest rivalry in tennis at the moment.

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Though Djokovic sealed the No. 1 ranking deal for the year when he advanced through his pool-play group without a loss, the two players seem ready to extend their rivalry into 2015.

Federer leads the head-to-head series 19-17 and won the last meeting in just over an hour and a half - a 6-4, 6-4 thumping of Djokovic last month at the Shanghai Masters.

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Djokovic won the previous meeting, the Wimbledon championship in July, in a thrilling, five-set match.

The players have met five times previously this season, Federer winning three - which helped the Swiss star rise from a No. 8 ranking at the beginning of the season.

According to barclaysatpworldtourfinals.com, Djokovic has won 31 straight matches and 14 straight matches at the World Tour Finals. He is seeking his third consecutive season-ending title. Djokovic defeated Nadal last year and Federer in 2012.

Djokovic's 61 matches won in 2014 marks the eighth straight year that he has won 60 or more matches.

Federer is gunning for an unprecedented seventh year-end title. He is the oldest player in 35 years to win 70 matches in a year and will finish this season with the most wins on tour. Federer currently has 72.

He has won six tournaments six times or more in his career - Halle (seven times), Wimbledon (seven), ATP World Tour Finals (six), Dubai (six), Cincinnati (six) and Basel (six).

Federer now will have finished in the top two in the world in 10 of the last 12 years - he failed to reach the top two only in 2011 and 2013.

Federer won't overtake Djokovic with a win, but he will narrow the points differential heading into 2015. He already has the most weeks at No. 1 at 302.

Whoever wins will get a leg up in 2015, but until Nadal returns and is healthy, the two loom as the dominant players in tennis.

Who will win Sunday's ATP World Tour Finals? Comment below or tell us @SportsWN.