1. Weak and strong eras

Federer fans will always point to his unmatched tally of 17 Grand Slams when arguing that he is the GOAT. However, it is certainly arguable that the majority of his titles came in a weaker era of tennis, making his tally somewhat misleading.

Between 2003 and 2007, Federer won 12 slams. Three came against Andy Roddick, who admits he is one of the worst ever players to hold the no.1 ranking.

One came against Lleyton Hewitt, who faded dramatically as tennis evolved into the physical, baseline-dominated game it has become.

Three came against Mark Philippoussis, Marat Safin and Marcos Baghdatis, who were ranked 48th, 86th and 54^th in the world respectively when Federer beat them in a final.

Federer won his first slam against the-then world no. 48 Mark Philippoussis (Picture: Getty)

He also beat a 35-year-old Andre Agassi in what was his last appearance in a major final, got two wins against an emerging-yet-still-raw Nadal, and beat Djokovic in 2007, when the Serb was an entirely different player to what he is now.

Since 2007, Federer has won just five slams, with another coming against Roddick, while he also clinched his only French Open title against the-then world no.25 Robin Soderling, who prevented the Swiss from having to beat Nadal on clay (something which Djokovic has since managed.)

Federer’s decline in terms of titles won coincides with the emergence of Nadal, Djokovic and, to a lesser extent, Andy Murray. Or, in other words, Federer’s decline coincides with the emergence of one of the strongest eras tennis has ever seen.

Federer boasts an overall finals record of 17 wins to 10 losses. But that is overshadowed when you compare it to his record of 3 wins to 9 losses in finals against Djokovic or Nadal.

Bear in mind too that Federer was 26 when his struggles against Djokovic and Nadal began, which detracts from the argument that only age has prevented him from competing as well as he once did.

By comparison, all but one of Djokovic’s major titles have come against Federer, Nadal or Murray. The average rankings of the players Federer and Djokovic have faced in finals also tells a story of its own: Federer’s stands at 16.3, while Djokovic’s is 6.5.

All but one of Djokovic’s slam wins have been against Federer, Nadal or Murray (Picture: Getty)

What can we take from this? Of c-o-u-r-s-e, no player can do anything other than beat what’s in front of them. The difference, though, is that Djokovic has had harder players in front him (including Federer himself).

Safin, Hewitt and Roddick do not hold a candle to Murray, Nadal and Djokovic, and the Swiss’ results show that.

Many will say that Djokovic must surpass Federer’s tally of 17 to be called the greatest ever.

He may well not do that (although he only needs to average two slams a year for the next four years), but even if he doesn’t reach that number, it is his achievements in a stronger era that mark him out as the GOAT.

2. The greatest season ever

Novak Djokovic’s 2015 is the greatest single season ever.

The Serb won 11 tournaments, three grand slams, was runner up at the French Open and finished with a win-loss record of 82-6.

Some will argue that Federer’s 2006 was better, when the Swiss won three slams, 12 tournaments and finished with a win-loss record of 92-5. However, as mentioned, 2006 was part of a significantly weaker era in the sport.

Djokovic’s 2015 is widely regarded to be the best season of all time (Picture: Getty)

Furthermore, when you rank tennis’ best players according to Elo, Djokovic’s level in 2015 is rated as the highest ever (in the Open era).

Elo is a rating system used to calculate the relative skill levels of players in competitor v competitor games. It was initially used to compare chess players, but can – and has – been adapted to tennis.

The system essentially works on a basis that if you beat a player you gain points and vice versa, with the number of points you win/lose dependent on the relative rankings of the player involved.

According to Elo, Djokovic hit the highest level ever attained during his 2015 season, one point ahead of Federer in 2007, suggesting that it is the Serb who is the best of all time.

3. King of the big four

This is the big one.

If we take head-to-head records as one of the main indicators of GOAT worthiness, then Novak is now the undisputed no. 1.

To be the best, you surely have to be able to beat those around you, and Djokovic’s four-set win over Federer on Thursday means he is now ahead in all his main rivalries.

For some context, Federer trails Nadal 23-11 in their head-to-head.

Furthermore, since Novak stepped up a gear in 2011, he has recovered from 13-6 down against Roger, winning six of their last eight meetings, and hasn’t lost to him in a Slam since Wimbledon 2012.

It’s widely agreed that the era of the ‘big-four’ is the strongest in tennis history, and if Djokovic sits at the top of that quartet, that makes him the GOAT by default, doesn’t it?

4. Potential

Let us remember that Djokovic is still only 28, yet is already firmly in the ‘best ever’ conversation.

The Serb is still in his prime, hasn’t even won the French Open yet, and potentially still has another five strong years ahead of him.

By that time, he c-o-u-l-d, and probably will, have completed the career slam, be closing in on Federer’s slam tally and have added to his burgeoning legacy.

One day, this will all be yours… (Picture: Getty)

That he is already being considered as one of the all-time greats midway through his career illustrates his greatness, and it’s scary to think what he c-o-u-l-d go on to achieve. Golden Slam this year, anyone?

5. Completeness

As renowned tennis coach Nick Bollettieri says, Novak Djokovic is the most complete player of all time.

He’s probably the best returner of all time, has the most impenetrable defence ever seen on a c-o-u-r-t, and his double-hander is the best all-round backhand on the tour at the moment.

The Serb has also vastly improved his serving, and while volleying isn’t his strong point (he’s still excellent at it, mind), he just doesn’t need to be given the quality of his baseline play.

Tennis has never seen defence like Djokovic’s (Picture: Getty)

If he does have a weakness, it’s the overhead smash, but then again, if you had to pick a shot to be rubbish at, it’d be that one.

All this has seen him develop into the most difficult-to-beat player around, and he will continue to take his game to unprecedented levels.

6. Always the villain

For some reason, Novak just isn’t loved.

While the standing ovation he received after losing the 2015 French Open final may grant him crowd-favourite status in Paris this year, the Serb constantly has to make do with being the villain of the piece.

At this year’s Australian Open alone he had his name spelled wrong at a ceremonial event and was accidentally cut from Lleyton Hewitt’s farewell video.

At the 2015 US Open final against Federer, he basically played an away match, contending with a 23,000 strong crowd all baying for the Swiss’ 18th title – listen, for example, to the reaction when Federer gets two break points deep into the fourth set.

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But as he always does, Djokovic keeps his cool, ignores the crowd, and wins the tournament. Djokovic faces scenes like this at nearly every tournament he plays, and it only serves to make his acheivements even more impressive.

Federer, meanwhile, has forever had the crowd on his side, and while that doesn’t detract from his own achievements, it can’t have made things harder for him.

The greatest rivalry in tennis history? (Picture: Getty)

There is no desire on anyone’s behalf to take anything away from Federer. He will forever be the sport’s greatest and most important ambassador, the master of reinventing yourself, and the most stylistically impressive player to watch.

Nadal is also certainly present in the debate, but his reliance on his clay c-o-u-r-t dominance and recent struggles have lowered his stock, leaving Federer and Djokovic as the standout candidates.

But it is the Serb who has now outstripped the Swiss. Back in 2006, Federer labelled Djokovic a ‘joke’ due to his apparent penchant for faking injuries in matches. Right now, it looks like Djokovic will have the last laugh.