In the two years from the 2011 to 2013 US Opens, Djokovic played 10 five-set Grand Slam matches. By comparison, Nadal has played 15 such matches in his entire 11-year career
Djokovic has a terrific chance to win multiple majors in 2014, because the game is in the midst of a potentially steep and interesting transition. Murray has beaten Djokovic in two of their past three Grand Slam final meetings, but Murray is coming off a back injury that hampered his title defense at Flushing Meadows and eventually required surgery. A healthy Murray, though, would further impede Djokovic at three of the four majors.
Federer is coming off his worst year in a decade, not just because he won only one title (the 250-level Wimbledon tuneup in Halle) but also because he went 0-7 against Djokovic, Nadal and Murray. His game creaked last year as matches extended into three and four sets.
He seemed not to have recovered from consecutive five-setters with Tsonga and Murray in Melbourne last year: He was trounced in straight sets by Tsonga at Roland Garros, lost in four sets in the second round at Wimbledon to Sergiy Stakhovsky and lost again in straights at Flushing Meadows in the fourth round to Tommy Robredo. Overall, Federer was just 3-6 in matches against top-10 players that went three sets or longer.
Outside of Nadal, del Potro is the most dangerous threat to Djokovic in the top 10. The Argentine beat Djokovic in the semifinals at Indian Wells, but Djokovic outlasted him in a classic Wimbledon semifinal and bested del Potro in a three-set final in the Shanghai Masters 1000.
However, del Potro beat all six top-10 players he faced (he did not play Tomas Berdych, Wawrinka or Tsonga) in 2013, and won the 2009 US Open. A healthy, focused del Potro can alter the look of any Grand Slam.
With Federer weakened and Murray's outlook uncertain, Djokovic needs to start adding to his major count. Perhaps sensing the urgency, he sought change and last month, he announced that six-time major champion Boris Becker would be his new head coach. (Marian Vajda, his coach since 2006, remains part of "the team.") After dominating in the past two seasons but failing to win a major after January, Djokovic clearly had some doubts about his process.
It's also fascinating to examine how close Djokovic came to winning both the career and calendar Grand Slam, yet ended up so far from both.
At Roland Garros, Djokovic lost just enough focus while up a break in the fifth to allow Nadal to escape. Djokovic accidentally touched the net following through on a smash, then as the match grew tighter, he complained about the watering of the court. Nadal did not blink and stole the match.
When Murray beat him at Wimbledon, Djokovic was clearly spent after his titanic five-set semifinal with del Potro, but Djokovic knows fatigue is no excuse. After all, at the Australian in 2012 he beat Murray in a 4-hour, 50-minute semifinal and came back to top Nadal in a 5-hour, 53-minute final. Djokovic also admitted personal-life distractions affected his play.