What's next for Djokovic-Nadal?

If Rafael Nadal and Novak Djokovic get tired of playing each other in Grand Slam finals, maybe they can try the X Games next. The two are establishing a kind of extreme tennis, one that pushes the physical boundaries of the sport and the conditions in which it's played.

Their Australian Open final ran 5 hours, 53 minutes. The machine-gun intensity of the points justified the time taken in between them. They were a little short of that pace in the first couple of sets of their French Open final, which came in at only about an hour apiece -- long in normal circumstances, but there is nothing normal about the Djokovic-Nadal rivalry.

Remember the epic 38-stroke rally between Richard Gasquet and Grigor Dimitrov at the French Open, which ended with Gasquet throwing up and Dimitrov collapsed on the floor with cramps? It was one of the many highlights of the first week.

Nadal and Djokovic played a 44-stroke rally during the final and carried on as if nothing much had happened.

Remember the epic five-setter between Paul-Henri Mathieu and John Isner that was 18-16 in the fifth set. That was 12 minutes shorter than Djokovic and Nadal's Australian Open meeting.

The pair's reputation for lengthy encounters is so well-established that tournament officials were berated in a news conference at the French Open for not moving up the 3 p.m. local start time for the final, given the weather forecast and the participants in the final. The officials protested that the prospect of playing up to 9:30 p.m. made the start time perfectly reasonable, but some skepticism remained. The start time may have been reasonable, but Djokovic versus Nadal rarely is.

The French Open final did not turn out to be about length. What would have been the big deal about another marathon anyway? The question in their latest encounter was not how long they could go, but how wet it could get.

As the steady drizzle continued and Nadal's grip on the contest steadily loosened, the match took on another fascinating dimension. This was rain tennis, a version of the game in which different forces of gravity and friction take over as the balls, weighed down with water and accumulating clay, become heavy and unresponsive on the soft, soggy court.

They played under the watery conditions for an hour and might have continued longer if not for Nadal, who had clearly had enough after losing eight straight games.

Then began the waiting game, possibly an even tougher mental challenge that called on the players to go to sleep while a Grand Slam final hung in the balance. "Seriously, I was very nervous during all the night," Nadal said.

When play resumed, so did Nadal's advantage. In a burst of frustration, Djokovic began banging his racket strings against his head, appearing to just avoid that infamous Mikhail Youzhny moment, whose self-inflicted bashing with his racket caused a heavy stream of blood to run down his head in Miami a few years ago. Djokovic had already vandalized his changeover bench the previous day, putting a hole in it when smashing his racket at the end of the second set. Nadal, not to be entirely left out, hit himself on the cheekbone with the trophy after the match.

If they meet at Wimbledon, what could be next? The Centre Court roof means no playing in the rain, but maybe they'll wear out all the grass, ending up with dirt-track tennis.

And it doesn't have to end there. The two are scheduled to play an exhibition for Nadal's charity in Real Madrid's stadium the week after Wimbledon, and Nadal has said he would be willing to return the favor by playing Djokovic in Serbia if asked. These types of events offer even more opportunities for extreme experiments, like the exhibition once played by Nadal and Roger Federer on a court made of half clay and half grass.

Perhaps in this one, Nadal could arrange for the tennis balls to be replaced by soccer balls, and Djokovic could extend an invitation to play on the slopes of his hometown ski resort.

There are endless possibilities. They could play on ice (Federer might sign up for that one). Or underwater, unless that's too close to the French Open final. Maybe a gravel pit, though according to Nadal and Djokovic, that seemed to be the surface used at Madrid this year.

Or maybe that's all quite unnecessary. Just give them a tennis court.