So at the end of it all - and as it has been for so many years - it is still Rafael Nadal and Roger Federer taking the two top slots in the rankings as the season ending ATP Tour finals ended in London on Sunday. And who would have expected this at the start of the year when Nadal was No 9 and Federer No 16 in the rankings?

But wait. It is not business as usual for the quartet known for long as ''The Big -Four’’ who dominated the tennis scene for the last few years. Novak Djokovic not too long ago the No 1 has fallen to No 12 while Andy Murray another player who knows what it is to be at the top has slid to No 16. So the wheel has really come full circle and only underlines the fact that in the intensely competitive field no one can take his place for granted.

Intensely competitive is apt for there are several players of the younger brigade who are making an impact and challenging the established stars. At the end of last year two of ''The Big Four’’ were out of the top eight; now two others are out of the top ten.

Grigor Dimitrov who won the ATP Tour finals and has risen to No 3 is clearly the leader of the pack but close behind would be the man who lost to him in the title clash David Goffin. The two would have been possibly the least expected pair to contest the final in London. After all when Goffin arrived in London he has never beaten Nadal or Federer and had never previously qualified for the ATP Tour finals outright – just a solo appearance as an alternate for the injured Gael Monfils last year a match in which he salvaged just three games from Djokovic. Dimitrov too had never qualified for the season finale being more familiar with London in the summer playing at Wimbledon (he was a semifinalist in 2014) or at Queen’s club.

And yet here was Goffin first getting the better of Nadal in the group stage and then ousting Federer in the semifinals for his first win in seven meetings with the Swiss legend. And here was Dimitrov ranked world No 40 in July last year contesting the final and winning it. Really no predictions can be made in the world of tennis given the rise of comparatively lesser known players and the fall of the superstars like Nadal and Federer last year and Djokovic and Murray this year.

Dimitrov a gifted 26-year-old Bulgarian has long been considered as one of the next big things in the tennis world and in fact earned the sobriquet ''Baby Fed’’. Over the last couple of years he remained in the middling category with the odd significant result or two but it was not until this year that the early promise was fulfilled. A first Tour title in 2-1/2 years in Brisbane, making the semifinals at the Australian Open, a title on home soil in Sofia, a maiden ATP World Tour Masters 1000 trophy in Cincinnati was followed by his biggest prize of his career in London. Potentially then he is the one to watch out for bigger things in 2018.

Belgium’s Goffin who turns 27 next month too has risen steadily and at London he became only the sixth player to defeat both Nadal and Federer in the same tournament. Indeed there was little to choose between the players in the rousing final that went to three sets and lasted 2-1/2 hours before Dimitrov won 7-5, 4-6, 6-3 to complete an all win record in his five matches and making him the first debutant to win the ATP Tour finals since Spain’s Alex Corretja in 1998. It was also his eighth career title and certainly his most significant.

But besides Dimitrov and Goffin there are several other players who have the potential to make it to the top. Alexander Zverev, Dominic Thiem, Marin Cilic and Jack Sock are among those who have made significant progress or have been in the top ten for quite a while and their chances cannot be disregarded. Then of course there are the already established stars like Stan Wawrinka, Juan Martin del Potro, Kei Nishikori, Tomas Berdych, Milos Raonic and Jo-Wilfried Tsonga who are still performing consistently despite being in most cases over 30. As TV expert commentator and former top ten player Brad Gilbert put it succinctly ''there is not a lot that separates the No 25th ranked player from No 3.’’ Almost any of these players can pull off a major upset or are capable of winning a Grand Slam title.

And of course let us not forget the aged superstars who are still winning Grand Slams. In fact Nadal and Federer shared the four titles between them and if they bounced back what prevents Murray and Djokovic from doing so?

Overall though despite Nadal occupying the No 1 spot this has been Federer’s year. At the start of the year he was being written off and in his 36th year having slipped to No 16 in the rankings who could have found fault with the doomsday pundits? And yet he extended his record career Grand Slam titles to 19 besides notching up several other notable achievements. Can be there any doubt as to his exalted status as the greatest player of all time?