LONDON (AP) There is one more match to play this season, and there is plenty riding on it for both Novak Djokovic and Roger Federer.

Djokovic, who has had the best season of his career with three Grand Slam titles, is looking to cap his incredible year by becoming the first man to win four straight titles at the ATP finals. Federer, however, can add to his record six titles on Sunday while also proving he can still beat the top-ranked Serb in big matches.

''When he's on, it's hard to play him,'' Djokovic said of Federer, who has reached his 10th final at the season-ending tournament for the top eight players in the world. ''We always play matches with a lot of tension. There is a lot at stake. I know I have to be on top in order to win against him.''

Djokovic reached the final by beating Rafael Nadal 6-3, 6-3 on Saturday. Federer advanced by defeating French Open champion Stan Wawrinka 7-5, 6-3.

Sunday's match at the O2 Arena will be the eighth meeting this season between the two players who hold a combined 27 Grand Slam titles. Djokovic leads 4-3 in 2015, including wins in the Wimbledon and U.S. Open finals, but Federer won in straight sets on Tuesday in the round robin stage.

''It's the same conditions, same court, same place,'' said Federer, who has handed Djokovic three of his six losses this year. ''For me it's an advantage because I guess it gives me a bit of confidence. For him it's an advantage because he gets a second chance, and he's in another final.''

Against Nadal on Saturday, Djokovic showed why he is the best player in the world. The 10-time major champion lost only seven points on his serve in the first set and three in the second. On the receiving end, he converted three of his five break points, including in the final game of the match.

''Novak for the moment is almost unbeatable,'' Nadal said. ''What Novak is doing is just amazing.''

Nadal tried just about everything to stay in the match, even hitting a ''tweener'' in the last game. Djokovic lobbed the ball over Nadal's head, but he chased it down and whipped a shot between his legs that made it back over the net. Fortunately for Djokovic, he was there to tap it back over and get the point.

The win evened the head-to-head record between the two players to 23-23, the first time Djokovic has managed to get level since the rivalry started in 2006. Their 46 meetings are the most between two players in the Open era.

Djokovic will have a chance to even the head-to-head series against Federer, too. Federer currently leads 22-21.

But the 17-time Grand Slam champion from Switzerland is considered by many to be the best indoor player in history. He has played in the semifinals at the season-ending event in 13 of his 14 appearances, advancing to the final 10 times. Last year, he withdrew from the final against Djokovic because of a back injury.

Trailing 3-2 against Wawrinka on Saturday, Federer quickly turned things around by breaking back to 4-4 and then reeled off five straight games to win the first set and take a 3-0 lead in the second.

''He has the perfect game against my game,'' said Wawrinka, the only man besides Djokovic to win a major this year. ''If you look today, it's not that I play really bad. I'm not tough enough mentally with myself, I'm not completely there.''

Djokovic will be there to face Federer in the final on Sunday. And even a loss won't dampen the season he has produced.

''Regardless of the outcome of tomorrow's match,'' Djokovic said, ''the season will still be the best that I had.''