Roger Federer will meet Novak Djokovic for the 43rd time in their careers when the duo square off for a place in the semifinals of the 2015 Barclays ATP World Tour Finals Tuesday in London. Even though Djokovic has been nearly unbeatable this season and with the 7,000-point ranking gap that the Serb currently holds against Federer, the 17-time Swiss grand slam champion believes that the former is incapable of being overcome.

Federer will play Djokovic in their second round robin match after winning their respective matches against Tomas Berdych 6-4 6-2 and Kei Nishikori 6-1 6-1. Despite the Serb’s amazing 2015 campaign, going into the season-ending tournament in London with a 23-match winning streak since claiming a 10th career grand slam title at Flushing Meadows in addition to a huge gap in the world rankings, Federer is not bothered about Djokovic’s nearly indomitable season.

“I don’t think I’m that far off,” Federer said, according tosc The Telegraph. “Then again, let’s speak in two days.”

Federer added that his match against the sensational Serb is not the one that he “cares the most about,” but also said that it will be a “very important” one. Federer also admitted that he had a bit of a careless start in his first round robin match against Berdych, who downed him 2-0 before turning the match around to take his first win in London.

The 34-year-old Swiss is hoping not to make the same mistakes he did when he play Djokovic next. The outcome of the match will determine the winner of their Stan Smith Group, which will advance to the semifinals.

Federer has handed Djokovic two of the Serb’s five losses this season. He beat Djokovic to claim the titles at the Dubai Duty Free Tennis Championships 6-3 7-5 and the Western & Southern Open 7-6(1) 6-3, two of the six tournaments that they went up against each other this year. Djokovic leads 4-2 in their head-to-head record this year including victories at the Wimbledon Championships and the US Open.

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