Should the tennis year, like the school year, begin in the fall? It’s starting to feel like that’s how it works on the men’s side. Since at least 2010, there have been two distinct seasons: The main one, which includes all of the Grand Slams, and ends with the U.S. Open; and then the rump one, which is played in October and November and ends up having less to do with what came before than it does with what comes afterward.

In 2010, Rafael Nadal won three majors and finished No. 1, but he won just one title after the U.S. Open. That left a door ajar, which Novak Djokovic eventually walked through by leading Serbia to its first Davis Cup championship to close the season. The win was important enough to help springboard Djokovic to No. 1, and three majors of his own, in 2011.

But what comes around goes around at the top of the ATP these days. By the fall of 2011, it was Djokovic’s turn to fade, and Roger Federer’s turn to fill the vacancy. Federer’s three titles that fall helped springboard him back to the top spot by July 2012. The pattern repeated itself a third time last fall, when Djokovic rose back up to win three fall tournaments and reclaim No. 1 from Federer, a position that Djokovic would hold until September 2013.

Are we having déjà vu all over again—again? It has looked that way so far this fall. As in 2010, Rafael Nadal dominated the Grand Slam section of the season, but he has faded just enough since then to let Djokovic gather momentum. The Serb has already won three tournaments since the U.S. Open and, as Rafa admitted yesterday, he's the favorite to win a fourth in London.

None of this should be surprising. With no more Slams on the schedule, and the No. 1 ranking either locked up or virtually locked up, the player who dominates for the first nine months must feel as if he’s done everything he needed to do that year, and that the fall is little more than an obligation. Nadal currently needs just one more win in London to secure his third year-end top ranking. He’s probably going to get it, considering that his next two matches will be against Stanislas Wawrinka and Tomas Berdych. His combined record against them since 2006 is 27-0.

What has been interesting this fall has been watching how the psychologies of the top guys have been affected by their relative positions on the ranking totem pole. It’s always amazing to see how delicate those psychologies are, and how quickly they can change, even among veteran champions. It also proves, if we needed it proven again, how success in tennis resides in the mind, rather than in the feet, the strokes, the serve, or anyplace else. With guys this good and this evenly matched, little changes in head space can mean everything.

Nadal's fall has pointed up how much his success depends on motivation. Numerous times in his autobiography, Rafa says that the only area of the game in which he feels like he has an edge on his opponents is the mental one. Considering how loath Nadal is to talk himself up in general, that means something. It has proven true again, at least on hard courts. Through the U.S. Open, he was 22-0 on the surface in 2013; since the Open, he’s 10-3. That’s not a huge drop, obviously, but as Rafa says, neither is his edge on most players. Other than on clay, Nadal has always been someone who succeeds by winning the big points and pulling out the close sets. That’s the mental advantage he talks about, and it comes from motivation as much as anything else. With a little less to play for this fall, Nadal has, unsurprisingly, not maintained the same level of motivation—it isn't something that can be manufactured, even by Rafa. In Beijing, Nadal lost to Djokovic after winning their three previous meetings this year; in Shanghai, he lost to Juan Martin del Potro for the first time since 2009; and in Paris he lost to David Ferrer for the first time in 10 matches.

Today, though, Nadal came back to beat a tired-looking Ferrer handily in London. It will be interesting to see Rafa's motivation level the rest of the week, and how much of it he can muster if he does clinch the top spot. He has already downplayed his chances in London, claiming he’s just happy to be there after missing the event in 2012. As if to prove his point, Rafa even showed up at the first press conference this week sipping a milkshake. Yet Nadal has a solid chance to win his first World Tour Final, and if he plays Djokovic over the weekend, he won’t want to take a second straight loss to him. After the last few seasons, Nadal must know that what happens in November doesn't necessarily stay in November.

Djokovic does, too. Psychologically, he has gone in the opposite direction from Rafa since their U.S. Open final. His loss that evening in New York, and his subsequent loss of the top ranking, have freed him up to play his best tennis of the year. Rather than having to defend his position, which is what the No. 1 player is always doing, he has gone on the attack again. The mental mood swings and moments of frustration and doubt that characterized his play in the biggest events in 2013 have largely vanished this fall. Djokovic began his career playing with a brash edge, and he began it by telling the world he was gunning to be the next No. 1. In that sense, Novak has returned to his roots: He’s hungry, and a little angry. It suits him.

For the last month, Djokovic has been on a self-proclaimed mission-nearly-impossible: To steal the year-end top spot from Nadal. He has kept the competition alive longer than anyone expected, but we’ll see what happens if and when Rafa finally does clinch No. 1 this week. Can Djokovic stay as hungry with a little less on the line, or will his thoughts stray ahead to Serbia’s Davis Cup final back home in Belgrade next weekend?

We’ll get an early indication on Tuesday, when Djokovic faces Federer for the second time in four days. Speaking of which, where is Fed’s head right now? He loves this time of year, and he also knows what it can mean for the following season. But in general, Federer doesn't seem overly affected by his place in the game at any given moment. As Federer said earlier this week, he has always believed that, no matter who the opponent is, the match is on his racquet; even at 32 and ranked No. 7, he still believes it.

At this point, Federer’s body seems more delicate than his mind. Last week in Bercy, he moved better than he has since the spring, and he recorded his biggest win of 2013, over del Potro. That’s all it took for the old Maestro’s confidence, and chutzpah, to return. How far will that confidence take him this time? We got our first answer last weekend, when he beat del Potro but couldn’t close out Djokovic. We’ll get our next answer when he faces Djokovic again this afternoon.

Finally, there’s one more player of psychological interest in London this week: del Potro, who may have the most to gain of anyone, from a confidence perspective. Now ranked No. 5, he seems to be back at the crossroads he faced in 2009: He has surpassed everyone but the Big 4, and he’s knocking, hard, on their collective door. But the door keeps getting pushed back in his face, and it will take a major psychological effort for Delpo to finally knock it down for good.

Since the Open, Del Potro has beaten Nadal in the Shanghai semis, before losing in a third-set tiebreaker to Djokovic in the final. He has beaten Federer in Basel before losing to him in Bercy. This week Delpo will face both Djokovic and Federer again. Can he establish himself as a clear-cut favorite over Federer in 2014? Can he put a seed of doubt in Djokovic's head, after losing two epics to him this year? The answers to those questions will affect del Potro’s expectations for himself at the big tournaments next year. And that’s key: For Delpo, the game is there, and so is the confidence that he can use it effectively against anyone. What's been missing against the Big 4 is the assumption of victory, the sense that, when he plays them, he should win.

For all of these players, London could be the springboard to a successful 2014. The off-season is around the corner, but like kids in school, the new year for the men has already begun.