End of Roger-Rafa as we know it?

I visited a bit the other day with Jelena Jankovic, who has been working out these days at her spiritual home, the IMG Nick Bollettieri Tennis Academy. Out of curiosity, I asked if she'd watched the ATP World Tour Finals.

"I did," she said. "I wanted to see how the men finish the year, and it looked to me like it was just like the women; they looked tired, and the round robin is always kind of strange. We're not used to winning a tournament after we lost in it, so when you have that, crazy things happen."

In other words, don't give the benefit of the doubt so quickly to the player who emerges as champion from the smoking ruins of another year-end round-robin battle. Whatever handwriting appears on the wall might be written in disappearing ink that will vanish by the time the first Grand Slam of the new year is played.

Still, Nikolay Davydenko's triumph in London might be more than a tribute to the little Russian's durability, determination and opportunism ... or the wacky nature of round-robin events. And the way Rafael Nadal disappeared, Roger Federer struggled every step of the way and Novak Djokovic ran out of gas -- while Juan Martin del Potro more or less duck-walked into the final -- added to the growing feeling that 2010 might be a year of transition.

To put this in perspective, consider that fewer than 11 months ago, men's tennis was still all about the Federer-Nadal rivalry; there seemed no end to it in sight. Nadal had just upped the ante by winning the Australian Open, which meant another routinely brilliant performance at Roland Garros would set up any of a number of related storylines: Could Roger Federer stop a Rafa calendar-year Grand Slam? Would Federer recapture his lost mojo with a typical mid-to-end-of-the-year push at the two tournaments where he fares best, Wimbledon and the U.S. Open? Would either or both men complete a career Grand Slam in 2009?

Only one of those narratives matured and came to fruition: Federer, surprisingly, completed his career Slam at the French Open after Nadal was upset by Robin Soderling in the fourth round. And by the time del Potro halted Federer's U.S. Open streak, the tennis landscape had been utterly transformed.

If you had to pick a moment when the game as we've come to know it exploded, it would be the upset of Nadal in Paris. It was no routine sensational upset, either, for it sent Nadal into a long hiatus to address his growing problem with knee tendinitis and enabled Federer to win that long-deferred first French Open title. And suddenly, the Roger-Rafa 24/7 rivalry ground to a halt.

But it turned out Federer wasn't able to satisfy the expectation that, absent Nadal, he would ride herd on the game. The idea that he would return to dominating form died at the U.S. Open. And by the end of the World Tour Finals, it was clear that Federer, like Nadal, was inhabiting a different, unfamiliar world, one full of struggles with focus and, perhaps, motivation, as well as young guns (Djokovic, del Potro and Soderling among them) and grizzled veterans (like Davydenko) eager to take anything the two icons wouldn't or couldn't grab.

As crazy as the WTF seemed, keep in mind there was no real reason for Federer to plead fatigue; he hardly played after the U.S. Open. Nadal, who benefited from a far smaller workload in '09, did not play like a well-rested contender hungry to take the fifth-most prestigious prize in men's tennis.

This year's WTF was a classic, in terms of chaos and the surprises those events generate. But explaining it away by saying the top players were worn out and hard-put to find motivation just isn't accurate.

We don't know what 2010 will be all about, but I'm pretty sure that for the first time in many years, it's not going to be about the Federer-Nadal rivalry.