Three slams, six defeats... so was Novak Djokovic's 2015 year the best season in tennis history?

On Sunday Djokovic defeated Roger Federer to win the ATP World Tour Finals for a record fourth time in succession, bringing to an end a phenomenal individual campaign in fittingly dominant fashion.

In total the world No. 1 won 11 tournaments in 2015, losing just six matches all season as he reached the final of every single tournament he entered bar one – his first of the year.

He won three of the four grand slams in the year (losing the French Open final, against most expectations, to Stan Wawrinka), dominating the field utterly in a manner that was nicely book-ended by his straight sets success over Federer on Sunday.

The statistics are certainly impressive. But was this the greatest individual tennis season ever compiled? We take a look at how it stacks up against some other contenders...

Grand slams won: Three (Australian Open, Wimbledon, US Open)

Total tournaments won: 15

Match record: 93-4

A winning record to match the very best, Connors did not triumph in France (a familiar refrain in this piece) but was otherwise untouchable around the world. At the US Open he dropped just two games in the final - which illustrates the gulf in class between him and the rest at that particular moment in time.

Why you might consider it the best: No-one has won more matches in a single year. The American won on four different surfaces (twice on carpet) over the season.

Why you might not consider it the best: Just one win on clay (in Indianapolis) may lead some to suggest he was not an all-round force, while some will question the quality of his opponents. His greatest career rival, John McEnroe, was just 15 at the time, while Bjorn Borg was 18 and only just emerging.

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Grand slams won: Two (Wimbledon, US Open)

Total tournaments won: 13

Match record: 82-3

From a purely statistical perspective no men's season matches this one from McEnroe: he won 96.47% of his matches in 1984. He lost just four games - and against Connors! - in the final of Wimbledon, while two of his three losses came in contests that perhaps mean less in the wider scheme of things. The other came at Roland Garros - where Ivan Lendl only beat him in five sets in the final.

Why you might consider it the best: In terms of winning percentage, no-one can rival McEnroe. He did not play the Australian Open (it still being a long way to travel at an awkward time of year at that time), lost narrowly in the French Open final – and his other two defeats came in a regulation tour event and the Davis Cup final (although it cost the US victory). He was dominant.

Why you might not consider it the best: The other contenders on this list would scoff at the idea of ‘only’ winning two majors in a year - and you could argue the main rivals we associate with McEnroe, Connors and Bjorn Borg, were not at their peaks.

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Grand slams won: Three (Australian Open, Wimbledon, US Open)

Total tournaments won: 12

Match record: 92-5

A perfect season was only denied by Rafael Nadal's victory over Federer at Roland Garros - something that, considering the Spaniard's subsequent record in Paris, perversely only seems to enhance Federer's achievements.

It is perhaps a measure of the calibre of his play during this phase of his career that it is difficult to actually pick out which calendar year was his best: He had a better winning percentage in 2005 and lost only a single match at Masters tournaments; but he won three slams in both 2006 and 2007 - so really his dominance was for three years rather than just one.

Why you might consider it the best: Many of the Swiss's supporters would suggest that statistics alone do not do justice to the artistry he displayed, raising tennis to a higher plane with his shot-making and imagination. It is perhaps also worth noting that a year before this 2006 high point he was similarly dominant, with a win/loss record of 82-4 - and he would also win three slams a year later too (only losing to Nadal in the French Open ... again). You can choose a number of Federer seasons for the purposes of this comparison, which is not true of all the other names.

Why you might not consider it the best: Some might suggest the strength of opposition in 2005 and 2006 was not what it would become only even a few years later - other than on clay. Nadal was still somewhat raw, Djokovic and Andy Murray were yet to emerge. That left Andy Roddick and Leyton Hewitt as his most fearsome challengers. Exactly.

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Grand slams won: Three (French Open, Wimbledon, US Open)

Total tournaments won: 10

Match record: 79-10

After being forced to retire due to injury against Andy Murray in the Australian Open, Nadal ripped off the next three slams without reply to establish himself at the peak of a sport that suddenly found itself blessed with three transcendent talents at the same time.

Why you might consider it the best: Three slam victories in a season speaks for itself (especially as injury, not defeat, stopped the fourth) and, in an era when Federer was at his best and Djokovic (whom he beat in the US Open final) was on the verge of becoming the sport's dominant force, is even more impressive in the context. Hindsight will look kindly on his achievements in 2010, even if the raw statistics are not as impressive as some others on this list.

Why you might not consider it the best: Some would argue that his 2008 season was actually better - even though he only won two slams, he reached a level of tennis perhaps no-one else has managed as he beat Federer, at his peak, in five-sets in one of the all-time Wimbledon finals. In 2010 he also lost to a variety of 'average' players along the way - Marcos Baghdatis, Guillermo Garcia-Lopez and Jurgen Melzer among them - and consequently was not as dominant on the ATP Tour as others have been.

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Grand slams won: Three (Australian Open, Wimbledon, US Open)

Total tournaments won: 11

Match record: 82-6

The Serbian moved to 10 grand slams for his career after notching three of them in 2015, although his loss in the final at Roland Garros - meaning the career grand slam still eludes him - will surely rankle for some time to come. That was his one obvious blemish on clay, however, a surface he notably seemed to bring up to the level of the others - perhaps his biggest leap forward on the season.

His 2011 campaign was remarkably similar, but the man himself is in no doubt this was his best effort.

“It’s the best year of my life," Djokovic said recently. "No question about it. Everything is working great."

Why you might consider it the best: The dominant man in a strong era for men’s tennis, the Serbian did it on all surfaces in 2015 – and for essentially the entire season too.

Why you might not consider it the best: The calendar grand slam managed to elude him, while six defeats is actually two more than he managed in 2011 (when he also won three slams). You might argue Federer and Nadal were actually stronger in 2011, too - although Djokovic was arguably not as rounded a player back then.

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Grand slams won: Four (Australian Open, French Open, Wimbledon, US Open)

Total tournaments won: 18

Match record: n/a

There's a reason he remains revered as one of the sport's all-time legends. If you were a tennis player in the 1960s you were pretty much resigned to second place ... and that is assuming you managed to be drawn on the opposite side of the tournament to Laver. Laver's first Grand Slam year in 1962 was remarkable in that he had only won two slam events prior to that season - losing far more finals (five) than he had won. Somewhere along the way he made the leap, and did not let up even as he was tested consistently by Roy Emerson (who lost three of the four finals to his compatriot). After turning pro in 1963, he took a while to dominate the pay-for-play ranks before sweeping the big three tournaments in 1967; and when the Open era began in 1968, he only won Wimbledon. But in 1969 it all came together: he won the only men's singles Grand Slam in the Open era, a quite amazing performance.

Why you might consider it the best: Who else has won all four slams in the same season? Laver's 1969 exploits have not been matched since the (men's) sport was fully open, and therefore all the top players of the day could have stopped him.

Why you might not consider it the best: You might argue that Laver himself had a better 1962. He won an extra four events (22 versus 18) and also helped Australia win the Davis Cup as well. In both instances, however, many would argue the depth of opposition is almost unrelated to what modern players have to deal with. Indeed, the sport as a whole might be almost incomparable now...

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Grand slams won: 3 (Australian Open, Wimbledon, US Open)

Total tournaments won: 16

Match record: 86-1

Navratilova's statistical achievements in 1983 stand up to anyone's challenge. To only lose once, across an entire season, is almost beyond comprehension - it is the sort of feat that some of the best players ever to grace a court have never even come close to matching in the 30 years since Martina did it.

Why you might consider it the best: Purely measured on the basis of winning percentage, no-one can touch Navratilova. And she only dropped nine sets all year!

Why you might not consider it the best: Her one defeat, in the fourth round of the French Open, means her grand slam record for the year is still not as strong as some of the others on the list. Does everything else make up for that?

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Grand slams won: 4 (Australian Open, French Open, Wimbledon, US Open)

Total tournaments won: 11

Match record: 73-3

Australian Open. Tick.
French Open. Tick.
Wimbledon. Tick.
US Open. Tick.
Olympic Games? Tick.

Graf in 1988 was a case of ticking all the boxes in a way no-one previously thought possible.

Why you might consider it the best: The only person to date to win the ‘golden slam’, she did not drop a game in the final of the French Open and came from a set and a break down against Navratilova at Wimbledon. She won in all sorts of ways in 1988.

Why you might not consider it the best: Her winning percentage does not quite match Navratilova’s, and she faded very slightly towards the end of the year (losing the year-ending tournament). Also, was the standard of opposition the highest? Navratilova and Evert were both coming to their ends, and the awesome Monica Seles was yet to emerge. As soon as she did, Graf looked very much beatable again.

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Not to weasel out of making a call after all that, but it would seem that opinions of the best individual season in tennis history will depend very much on your what criteria you place the greatest emphasis on.

Are the grand slams the be-all and end-all? Then Rod Laver and Steffi Graf are way out in front. Is winning record the priority statistic? Then McEnroe edges the field, or even Navratilova.

However, if you believe that tournament success across all surfaces and sustained throughout the whole year is more significant than simply slams and victories? Then Djokovic's 2015 campaign is certainly in the mix.

The whole debate is complicated further, though, if you feel the strength of opposition is another important factor to be weighed up. That opens up a whole new debate that is almost impossible to quantify (good luck definitively working out whether Federer was a better player in 2012 than 2010, for example, and if so by how much).

In broad strokes, however, you would have to argue that the modern era trio of Nadal, Federer and Djokovic face stronger opposition than any of their historical rivals. That means Djokovic's just completed campaign definitely warrants serious consideration; yet it also suggests that his 2011 campaign, when Federer and Nadal were both closer to their best, might have been better after all. But the man himself says that this has been his best year - and who are we to argue?