No. 1 Novak Djokovic stares down No. 3 and arch nemesis Roger Federer in Tuesday’s ATP World Tour Finals clash at London’s O2 Arena. The two tennis stars are in Group Stan Smith in the round-robin tournament. 

Both Djokovic and Federer defeated their first opponents in straight sets on Sunday. Federer defeated Tomas Berdych 6-4 6-2 in almost one hour and 10 minutes, while, Djokovic needed one hour and five minutes to defeat Kei Nishikori 6-1 6-1.

Marking the end of the season, Djokovic looks for his fifth victory over Federer this year, but the Swiss legend also gotten the better of the world’s top ranked player twice this season with the last coming at the Cincinnati Masters.

All told one of tennis’ greatest rivalries sits at 21-21, though Djokovic has taken four of the last six meetings, including the U.S Open final in four sets 6-4 5-7 6-4 6-4. In a solid all-around performance, the Serb generated 54 unforced errors out of Federer, but Federer also fired off his big serve for 11 aces.

Beating perhaps the biggest foe of his career would cap 2015 well for Djokovic. Along with taking the U.S. for the second time in his career he captured two other slams, Wimbledon and Australian Open, and reached the French finals.

The 34-year-old Federer also posted a solid 59-10 record throughout the season while claiming six singles titles.

Start Time: 3 p.m. ET

TV Channel: Tennis Channel

Live Online: Tennis Channel Everywhere

Prediction: Djokovic in 3 sets