In recent years, tennis fans have become accustomed to seeing Roger Federer and Rafael Nadal invariably meeting in almost every Grand Slam final year-after-year, but are the tides changing?
The pair have fallen to fifth and fourth respectively in the ATP world rankings, with David Ferrer occupying third place, the first time any man other than Federer, Nadal, Murray and Djokovic has been in the top three since 2006.
It seems that Rafa is really struggling with a knee injury that kept him out of the game for seven months last year including the Australian Open 2013 and US Open 2012.
When the Spaniard came back from the knee problems, many questioned whether he had what it took to compete, but he answered the critics in emphatic fashion by losing only two matches in Miami and Vina del Mar before winning the French Open comfortably.
However, the 27-year-old disappointed with a first round Wimbledon exit to lowly ranked Belgian Steve Darcis, leading to questions over his condition.
On the other hand, Roger Federer has remained injury free throughout his career, but it seems that father time may be catching up with the man who is considered by many to be the best player of all time.
Federer has won a record 17 Grand Slam titles, but has slumped out of the last two earlier than expected, with Tsonga overpowering the Swiss in the French Open quarter final and suffering the most shocking of shock defeats in Wimbledon's second round to Sergiy Stakhovsky.
For the most dominant grass court player of the open era to fall so early on his favourite courts is what has lead many to question whether the world number five should call it a day.
However, I believe it is premature to question Federer's age as a reason for his poor season. It is obvious that he isn't as invincible as he once was, but the 31-year-old is facing a generation of hard hitting players that he didn't have to face during his period of dominance.
With the style of the game changing, it is much more likely that upsets will occur, especially if the top players are not quite at the top of their game.
The question now is, why have the upsets only effected Federer and Nadal, while Murray and Djokovic are as impenetrable as ever?
Well, plainly speaking, the two younger members of the "big four" are playing exceptional tennis and while the pair have encountered difficulties on their way to each of their grand slam successes, they have managed to come through with excellent defensive qualities and ability to counter punch, something Federer is struggling with because he isn't as quick as he once was and Nadal is strugglng with because of his dodgy knees.
For me, Murray and Djokovic have all the necessary tools to compete in the harder hitting form that the game is taking a turn towards, however i'd say the dominance of the pair won't be as secure as the era when 33 of 34 grand slams were won by members of the big four.
Younger players like Jerzy Janowicz and Grigor Dimitrov have shown the talent necessary to beat these big players and go deep into tournaments. If they develop we could even be talking about two big four replacements in the making.
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