Since the World Tour Finals positioned itself in London in 2009, the names making up the event have remained very much the same. 2013 looks to be no different with little alteration of the rankings possible from the remaining events to truly change the lineup.

Over the last five years, the names of those who qualify for the World Tour Finals have revealed  very little movement within the top echelons of the game. Granted, a few minor shuffles have occurred, involving the likes of Mardy Fish, Janko Tipsarevic and Fernando Verdasco. These are good players in their own right who can crack the top 10, but not game changers who have the ability to stick around.

John McEnroe claimed in his book Serious that Arthur Ashe once remarked that the difference between players ranked No. 10 and No. 5 is the same as the difference between players ranked No. 100 and No. 10. Ashe continued that going from fifth to fourth is like going from tenth to fifth, and that reaching third or higher is virtually inconceivable.

The Arthur Ashe statement puts into perspective what Rafael Nadal has accomplished this year, after many observers had counted him out. Coming back from almost a year away and beating almost everyone in his path, while reclaiming the number one spot, will go down as one of the most stunning achievements in a stunning career.

Going up is one thing, sliding down is another and a whole lot less fun.

The top four had been the Big Four of Nadal, Novak Djokovic, Roger Federer, and Andy Murray until this year. At this stage last year, in fact, Roger Federer still held the No. 1 ranking. Twelve months later, after a dismal season, he has not yet clinched a berth in the World Tour Finals—a tournament that he has won more often than any man before him. Although his name still brings in the crowds, Federer’s game no longer strikes fear into his peers.

Fellow Swiss Stanislas Wawrinka has produced a year quite the opposite of Federer’s nightmare, having climbed from 17th place at this time last year, to a current ranking of No. 8. Wawrinka reached his first major semifinal this year and has notched seven victories over top-10 opponents, more than anyone except Nadal and Djokovic.

Nevertheless, Wawrinka will not rank among the favorites to win the year-end championships, assuming that he qualifies. Even regular attendees to the event, Tomas Berdych, Jo-Wilfred Tsonga and David Ferrer, would be hard-pressed to dominate that elite field. All of them have notable flaws, whether physical or mental, that a Nadal or a Djokovic can exploit. Milos Raonic and Richard Gasquet, who eye a an outside chance to qualify, appear of the same mould.

World No. 5 Juan Martin Del Potro, the only active man outside the Big Four who has won a major, is showing genuine form having won recently in Tokyo. That said,  the finalist at the 2009 year-end championships still has not claimed a title at the Masters 1000 level.

This absence of credible competition in the layer just below the elite leaves Rafael Nadal and Novak Djokovic on a collision course for a final meeting in whatever tournament they both appear, especially with Andy Murray absent with an injury. The only time to cast a bet against either of them?  When one of them faces the other.