So utterly have the "Fab Four" dominated men's tennis this year that it would seem foolhardy to look beyond Novak Djokovic, Rafael Nadal, Andy Murray and Roger Federer in predicting the winner of the glittering finale to the 2011 season, the Barclays ATP World Tour Finals at London's O2 Arena.
This year, for the first time, all four Grand Slams and all nine of the Masters 1000 titles have been shared by those four, with Djokovic leading the charge in record-shattering fashion by capturing three Grand Slams (Australia, Wimbledon and the US) and five Masters crowns. Not since Stefan Edberg, Boris Becker, Ivan Lendl and Andre Agassi were in their pomp in 1990 have the sport's riches been in the hands of such an elite group.
So it is just as well, and thoroughly appropriate, that Roger Federer, the defending champion and Grand Slam record holder, should provide a word of caution before battle commences on Sunday afternoon among this elite eight-man field. After all, when this prestigious tournament came to London for the first time in its five-year run in 2009 the crown was snatched by the unfancied sixth seed, Nikolay Davydenko, who saw off Nadal and Federer before beating Argentina's Juan Martin del Potro in the final.
Federer thinks that the four who are widely seen as merely making up the field - David Ferrer, Jo-Wilfried Tsonga, Tomas Berdych and Mardy Fish - are in with a shout. "I don't feel like those four have no chance," he said after winning the Masters at Bercy Stadium, Paris, last weekend. "I definitely could see something like [Davydenko] happening again this year."
The decisive factors will be freshness and fitness after a draining year, and as Federer went on to point out, "Fish and Djokovic at this point look a little bit weary". Both fell prey to injury in Paris a week ago, whereas Federer took a break after the US Open and then bounced back to win in his home city, Basel, and then Paris, which means he will open the World Tour Finals on Sunday against Tsonga on the back of a 12-match winning streak.
Quite apart from the $1,600,000 cheque on offer for anyone emerging from the London week as undefeated champion in both the group matches and knock-out stages, there are other incentives for Federer to repeat that 2010 triumph. The Swiss stands level in the record books with Lendl and Pete Sampras as a five-time Masters champion, so another title would reinforce his bid to be acknowledged the best ever. Victory would also tend to silence the mutterings that Federer, fourth in the world rankings, is past his best nowadays.
Undoubtedly the biggest question mark hangs over the fitness of Djokovic, whose body finally seems to be exacting a price for that that astonishing year. He comes to London having won 69 of his 73 matches in 2011. The 24 year-old Serb reeled off 44 straight victories and seven titles before being halted by Federer in the Roland Garros semi-finals, then claimed his most cherished prize at Wimbledon.
The first indication of trouble with the shoulder of his serving arm came at the Masters event in Cincinnati, where he retired at a set and 3-0 down to Murray in the final. Even though he went on to claim the US Open he was clearly in trouble with the shoulder and it has since forced his retirement to Del Potro in their Davis Cup semi-final, and from the quarter-finals in Paris last week. In between those events Djokovic was beaten by Kei Nishikori in the Basel semi-finals, dropping the final set 6-0.
Then there is Nadal, runner-up in London last year and still waiting for his first success in this event. The Spaniard, who has suffered more than his share of grief with injuries to knees and feet, pulled out of Paris in a bid to ensure full fitness for London and the Davis Cup final. We may have a better idea of how fit he is for the final hurdle of 2011 after Sunday evening's match against Fish, nowadays the top-ranked American but whose fitness is also in question because of a hamstring problem.
For fitness and freshness, Federer and Murray are the form horses. "I have had some really tough losses this year," said Federer, who failed to win a Grand Slam in 2011. "But I kept believing the year wasn't over and now I have a massive highlight coming up."
Murray, too, is in fine fettle, despite having pulled out of Basel with a slight strain. His autumn run of 18 wins and three titles was halted by Berdych in the Paris quarters but he is determined to go one better than 2010 in London, when he lost the semi-final to Nadal, a candidate for the finest three-set match of the year.
"I am happy with my form," Murray declared. And should he go the distance and win his first World Tour Finals title there will be thousands of followers in the O2 Arena who will share that happiness.