This year’s ATP World Tour Finals have largely followed a familiar pattern, with the best players in the world – Roger Federer and Novak Djokovic – qualifying with ease from their groups, and the weakest players in the draw – Tomas Berdych and David Ferrer – losing all three matches and looking out of their depth.

The key difference this time, however, is the return to form of Rafael Nadal, who sealed only his second season-ending semifinal appearance in the last five years with a three-set victory over countryman David Ferrer. Nadal comfortably beat Andy Murray and Stan Wawrinka in his other two round-robin matches, and, whatever happens in his Saturday encounter with Djokovic, his resurgence this week suggests he will have a much better year in 2016 than he has had in 2015.

Fan favorite Roger Federer continues to defy his advancing age and has played superb tennis this week to win all three of his round-robin matches and book his place in the last four. His straight-sets victory over Djokovic was particularly impressive, and it is probably a feat he will need to repeat on Sunday evening if he is to lift an incredible seventh ATP World Tour Finals trophy. It was his third win over Djokovic this year, and he remains the only player to beat the Serb more than once in 2015.

Losing to Federer ended three extraordinary winning runs for Djokovic. Before the match, the world number one had won 38 consecutive matches on indoor courts, 23 matches in a row on all surfaces since the Cincinnati final in August, and 15 straight matches at the ATP World Tour Finals. Such records, along with his astonishing overall performances in 2015, were starting to give the Serb an air of invincibility, and his rivals were doubtless relieved to see him finally lose. However, the defeat may even make him hungrier to claim his fifth season-ending title (and fourth straight) on Sunday night.

A heavyweight clash this evening between Murray and Wawrinka will decide the fourth semifinalist, and a win for either could provide an important confidence boost ahead of the Australian Open in January, as well as an outside chance to win the event. On current form, the Swiss No. 2 arguably goes into the clash as the slight favorite, especially since he has reached the semifinal stage of the World Tour Finals in each of the last two years. But Murray won’t go down without a fight, and he will probably have plenty of tricks up his sleeve ready for tonight. There is very little between the players in terms of ability, so the potential is there for a classic encounter at the O2 Arena.

Kei Nishikori was the unluckiest player in the draw for this year’s World Tour Finals. Had he been in the other group and avoided Federer and Djokovic, he could have qualified for the last four. As things were, he put in a very creditable effort, beating Berdych in a high-quality match, pushing Federer close in a tense three-set match, and losing to Djokovic when the Serb was playing close to his best. The Japanese star is capable of great things on a tennis court but struggles with injuries, so if he can stay fitter for longer next year he could be a serious contender for the major tournaments.