How High Can Djokovic Climb on the Grand Slam Title List?

With his Wimbledon title Novak Djokovic now has nine grand slam singles titles to his name, and there's no reason to believe he can't add several more to his total.  He'll be the heavy favorite to get his tenth at the US Open, and should have a good chance at further adding to his total in Australia after that.  While it's risky to predict that anyone will win five more grand slam titles, it doesn't seem crazy to think Djokovic could make a run at Rafael Nadal and Pete Sampras' total of 14. 

While Djokovic just turned 28, he appears to have at least a few years remaining in which he can rack up multiple grand slams per year.  The rest of the Big Four isn't nearly as much of threat to his slam chances as they used to be, and it's not clear who else is going to stop him.  Federer is nearly 34, and if he didn't beat Djokovic at Wimbledon it's hard to see where he's going to beat him.  Djokovic has solved the Nadal riddle as well, as he dispatched him easily at Roland Garros and has beaten him 6 out of the last 7 times.  He also has been dominant against Murray, having beaten him 8 straight times.  Wawrinka has given him trouble as of late (most notably denying him the career grand slam at the French Open), but Wawrinka is inconsistent and often loses earlier in tournaments. 

It's true things can change quickly in tennis, as a player can be on top of the world one moment and then quickly fall down a few pegs without much warning.  Nadal's decline has been pretty drastic, and he's only one year older than Djokovic.  However, Djokovic isn't showing any signs of slowing down, and it's hard to see his level of play dropping much in the next two years.  

Fortunately for Djokovic, there's not a particularly strong group of younger players ready to knock him off his perch either.  There's simply not many players in the 23-26 age group who look like they're ready to become a serious challenger to the world number one.  Cilic, Nishikori, Raonic and Dimitrov are all very good players, but they're up and down, injury prone and simply not at Djokovic's level.  While there's a more talented group of younger players on their way up (i.e. Kyrgios, Thiem, Coric, Kokkinakis, etc), they're probably a couple years away from hitting their peaks and won't be much of a threat to Djokovic anytime soon. 

Even if Djokovic doesn't age as gracefully as Federer, if he can remain at this level until he's 30 we may be viewing him in an entirely different light at the end of his career.  It always seemed like Djokovic was going to end up in the same conversation with the likes of Agassi, Lendl, Connors, Borg, and a few others who are considered legends but not quite in league with Federer, Sampras, Nadal, Laver and Emerson.  He's still got some work to do, but it looks like he may get a lot closer to joining that latter quintet than many of us thought.