This is the first in a series on the intriguing storylines coming into 2010. I’ll begin with the biggest question on the men’s tour as the new season begins: Can Rafa regain his No. 1 form?

Over the holidays and through the off-season I try to watch as little tennis as possible. But last week, flipping idly through the normally barren upper channels on my TV, I happened on a few games that no fan of the sport should ever turn off. ESPN Classic, in its Best of the Decade series, was replaying the 2008 Wimbledon men’s final, and the score was 3-4, Rafael Nadal serving to Roger Federer, in the fifth.

This was before the match had been sealed with its Greatest Of All Time label, when no one had any idea how it would end, when it looked like it might just be the story of Federer’s crowning moment, the improbable comeback his career still lacked at that point (now we know that it would have to wait until the following year’s French Open). Nadal went down 30-40 on his serve. This was essentially a championship point, considering that Federer hadn’t been broken for three sets and about five hours. Nadal hit his first serve in and Federer hit a decent return down the middle. It looked like a normal crosscourt rally was about to ensue. Instead Nadal stepped around the ball and broke open the point with an inside-out forehand. Scrambling, Federer could only throw up a desperation lob. Nadal put the overhead and the break point away.

Federer would subsequently hold for 5-4, forcing Nadal to serve to stay in a match that had once seemed sure to be his. On the first point, Nadal missed his first serve. As Nadal began his second-serve toss, Federer, sensing this was the moment to go for the kill, moved aggressively forward and toward his backhand side, the spot where he assumed the second serve would go. Except that it didn’t go there. Nadal tossed the ball a little farther behind his head and did something he had done only a few other times that day in the deuce court: He hit his second serve out to the forehand side. Federer, caught, nowhere near it, was aced. He dropped his head, looking almost embarrassed. It wasn’t his moment after all. Nadal held.

I’d forgotten about those two shots, the forehand and the serve. Seeing them again made me think two things. (1) Any idea that this match ended up as a crapshoot in the dark, that it was little more than good fortune that elevated Nadal over Federer that day, is nonsense. At the end, late in the fifth set, he was both the gutsier and the smarter player. (2) Nadal is, more than any other Hall of Fame player I’ve seen, a creature of confidence.

The Wimbledon final, along with his performance at the Olympics the next month, marked a pinnacle of belief for Nadal. He’d dominated the sport, and Federer, through the clay-court season, and the momentum from those wins was enough to carry him to his biggest titles yet on grass and hard courts. As Federer judiciously described Nadal’s 2008 season: “He was the man of the moment.” Of course, Nadal isn't the only tennis player who lives on confidence, and it’s obvious that you have to feel pretty good about your game to go for an inside-out forehand winner down break point in the fifth set of the Wimbledon final. But confidence means even more to Nadal than it does to just about everyone else. Even his resourcefulness, his on-court intelligence and thinking process, are dependent on it. By the end of 2009, when Nadal had no belief in himself whatsoever, it wasn’t just that he'd stopped hitting the ball well. What was strange was that he wasn’t using all of his mental and strategic resources to try to turn matches around. At the final event in London, where he lost six straight sets, Nadal did little more than get to the ball and hit it back over the net. Like I said, it’s hard to think of other players of his stature whose level—whose belief, mood, even the effectiveness of his signature shots—varies so wildly.

The question now is, can Nadal climb back to those peaks of confidence that he reached in his “man of the moment” summer of 2008? And if so, how long will it take?

Since his breakthrough season of 2005, Nadal has typically been unbeatable for stretches of four to six months before falling back to earth for about the same amount of time. Maybe, on second thought, Nadal isn’t unique for his varying levels of confidence, but for how consistently he varies from year to year—he always goes up, he always goes down, and then, just when you wonder whether his psyche or knees are permanently fried, he always goes up again. Before 2009, Nadal’s hot streak usually started with the clay-court season, or just before it at Indian Wells, and sustained him until the dog days and hard courts of summer in North America. Last year, it started earlier, in Australia in January, but lasted about the same amount of time, until the end of May in Paris.

If it hadn’t been for that slightly surprising start last year, I would say with confidence that it will be a while before we see the Nadal of Wimbledon 2008; that he’ll need to get matches and wins under his belt to build himself back up. But even before last season, Nadal’s turnarounds could be sudden and unexpected. In 2007, he started so slowly that, for the first time that I could remember, I didn’t pick him to reach the semis of a Masters event, at Indian Wells. Naturally, he chose that tournament to play his finest tennis in months. He blew through the draw and won virtually everything before being stopped in five sets in the Wimbledon final by Federer. (I’m betting that more than one of you will say that all Nadal needs is for me not to pick him to win a major, and everything will be all right for him.) As he showed in Indian Wells that year and in Melbourne in 2009, Nadal doesn’t necessarily need to work his way up to his best tennis. He can get there in the course of about a week.

Has Rafa shown any signs of his old form this week, in his two early round wins in Doha? I caught about a set of his match against Simone Bollelli, and I thought he looked OK. He stepped around a few forehands, but not as many as he does when he’s feeling good. He hit a few backhand winners, but he also hit some so poorly that he was doing shadow backhand swings after missing them, telling himself to extend through the stroke more. He was spending most of his time well behind the baseline. Overall, he seemed to be closer to late 2009 form than prime 2008 form (the orange shirt doesn't help, either), though he showed much more determination than he did in London. After his long, involuntary mid-season '09 break, he didn’t want to take any more time off at the end of the year. You could see against Bollelli that Nadal wants to work his way out of this slump.

We can’t know the future, but if we take the past as a guide—what else can we do?—we can only say that Nadal will reach his best form sometime in 2009, and that he’ll stand at the center of at least one Grand Slam winner’s circle. He’s been there in each of the last four seasons, a period of time in which he’s never fallen out of the Top 3. He owns winning records against virtually every player of consequence. And there are question marks surrounding the other guys near him in the rankings: Can Djokovic keep it together for two full weeks? Can Murray become more proactive? What’s Federer’s motivation now? Is del Potro ready to shoulder the expectations? 

While the Federer-Nadal chokehold at the top of the sport will end someday, it has already proven to be a uniquely durable two-man product. Each of them has wavered over the years, each has seemed to be on his last legs—literally, in Nadal’s case—but neither has been dislodged from the year-end No. 1 or 2 spot since 2004. At some point, you have to say of their predicted demise: I’ll believe it when I see it.

Nadal’s 2010 will depend on one long-term element and one short-term element. The long-term issue will be his knees; he’s playing a similar schedule to last season, when they betrayed him halfway into the year. The short term issue will be his ability to find that match, that moment, that shot, that tournament, the one which will allow him to find his old confidence, his old aggressiveness, and his old resourcefulness and become temporarily unbeatable again.

In the meantime, tennis fans can enjoy watching him search for that moment. Nadal’s ups and downs make him, more than most other players, worth watching for the journey as much as for the end result. Where Federer, the ultimate in consistent excellence, barely lets us see him sweat, Nadal takes us for a ride with him as he plays—sometimes it's scary, other times it's exhilarating. The guy has the gift of transparency; few, if any, current players photograph as vividly on court. In his walk, in his face, in his eyebrows, even in his backhand, he can’t hide how he’s feeling. I’ll predict just one thing about Rafa in 2010: He’ll be a player to watch.