Rest of Big Four no longer a threat to Djokovic's reign

When Novak Djokovic leaves for the ATP World Tour Finals in London beginning next week, he ought to pack his thermal bag with a hammer, not those tennis rackets. For he'll probably be driving the final nail into the "Big Four" rivalry.

True, this celebrated and accomplished quartet is still going to sell a lot of tickets, as will Tomas Berdych -- provided he goes and sits in the ticket booth. But the theme of 2015 in tennis at the homestretch has been Djokovic's systematic dismantling of the Big Four as a four-part rivalry -- the latest a thorough beatdown of Andy Murray in Sunday's Paris Masters final.

So let's take a look at how the four men in question brought the game to this juncture:

No. 5 Rafael Nadal: The ranking already tells you a lot. Stan Wawrinka is now ensconced at No. 4, and Nadal is thankful to have climbed back up into the top five.

A fluky back injury had played a part in Nadal's failure against Wawrinka in the Australian Open final of 2014. Thus, the first Grand Slam of 2015 seemed the perfect place for Nadal to hit the reset button. He had taken off most of the fall of 2014, so the conventional wisdom dictated that he was well-rested and ready to resume his epic rivalry with Djokovic.

Instead, Nadal floundered, week after week, month after month, through most of 2015. He ended up in a heated rivalry with ... Fabio Fognini.

Going to London, Nadal is 4-10 against top-10 players this year and 0-5 against fellow Big Four members this season. Djokovic accounted for three of those losses.

No. 3 Roger Federer: With Federer already 33 at the beginning of the year, age alone applied a question mark to his name. But what a surprise -- and inspiration -- he turned out to be. Put it this way: Imagine what the year, and the rankings, might have looked like had Djokovic decided to spend the year in Thailand, studying, instead of just talking about Buddhism?

But Djokovic had his priorities straight. He denied Federer two Grand Slam titles in the finals of Wimbledon and the US Open. Federer clearly was the class of the field after Djokovic at both those events. Up for discussion: Would Federer have come up with that highly entertaining -- and effective -- Sneak Attack by Roger (SABR) tactic were he not desperate to crack the Djokovic code?

Federer is 15-5 against top-10 opponents this year. But consider this: He didn't lose to a single opponent in that category other than Djokovic, and he accounted for two of Djokovic's five losses thus far in 2015.

No. 2 Andy Murray: It tells you something about the weakness in the very foundation of the Big Four that the man ranked highest behind Djokovic is also the one who's been least successful against him.

That's not a great sign, because Djokovic and Murray were theoretically meant to replace Federer and Nadal in the rivalry hall of fame. They're both 28, with Murray born just a week before Djokovic.

Murray is 12-10 against top-10 opponents this season but 2-9 against the Big Four. Murray's major problem is that this was Djokovic's 10th win in their past 11 meetings, and it brings Djokovic's head-to-head lead in the rivalry with Murray to 21-9.

"I feel like I need to start doing things better. ... The score line in the last couple of matches there hasn't been good," Murray told the media after Sunday's loss at the Paris Masters.

No. 1 Novak Djokovic: By the end of the World Tour Finals, Djokovic could join Federer on the list featuring the five best annual winning percentages of the Open era. The other names on that list? John McEnroe and Jimmy Connors. (Federer is there twice.) Djokovic is fifth at 93.98 percent, on the strength of a 78-5 record, with 10 titles.

The margins in that category are razor thin. A single loss in London, even in the round-robin portion, and Djokovic tumbles out of his spot. That's one more way in which Federer is being nicely set up in London as the spoiler. He probably doesn't love that role, but these days, everyone -- including three of the Big Four -- has to take anything Djokovic gives him.