After Nadal lost seven straight finals to Djokovic between 2011 and 2012, Nadal was forced to completely retool major portions of his game. He needed more free points from his serve. He could escape against other players, Federer included, with less depth on his groundstrokes, compensating with spin and placement. But short replies cost him dearly against Djokovic, who has been untroubled by the height of Nadal's ball to his backhand, able to redirect a ball that vexes the rest of the tour down the line for a winner.
Djokovic's loss to Nadal in the 2010 US Open final was the first springboard (Serbia's Davis Cup win was the other) to his rededication to and refocusing on his game. It was Nadal who best exposed Djokovic's lack of belief during the most crucial times. Djokovic learned he could not rely on the weapons he would need to become a transcendent player. But that all changed. The result was a 70-6 2011 with three majors for the Serb.
After his losses, Nadal readjusted following the 2012 final in Melbourne, and the result has been a mesmerizing test of wills between the two players. Nadal has beaten Djokovic with a champion's combination of adjustment and determination. Nadal's backhand, curiously short and vulnerable traditionally, has become a weapon for Nadal, who now steps in and uses it frequently as a finishing shot. Nadal, one of the game's best volleyers, now comes to the net often, providing variation and a willingness to attack and end points. These adjustments have virtually all come in response to the Djokovic onslaught. Each has made the other better, more formidable, more dangerous.
Although Nadal attacks the court with more aggression and play inside the baseline, he has also forced Djokovic -- the man of the iron will -- to blink. Djokovic double-faulted on match point to give Nadal the title in the French Open final in 2012 and oddly lost his composure at Roland Garros last year, complaining about the grounds crew and its timing in watering (or not watering) the clay. It was a psychological slip that unraveled Djokovic and toughened up Nadal.
After it appeared Djokovic had begun to control the match in the 2013 US Open final, Nadal grounded Djokovic into wild mistakes from which he could not recover, losing 6-1 in the fourth and final set.
The Australian Open is the beginning for these two, but not the end. Nadal and Djokovic play their matches with a kind of Promethean importance, similar to the Nadal-Federer matches of old. They play with the knowledge that they are the two best players in the world, and their intensity carries the rest of the sport.