LONDON—I attempted a thought experiment during the Federer-Nadal match last night. (A thought experiment is just like a real scientific experiment, except it’s much cheaper and nobody can tell you that you got your results wrong.) I tried to imagine that I was an alien—stick with me here—who knew the rules of tennis but nothing else; an alien observing these two men wearing similar styles of clothing, bearing identical symbols, much the same age and build, and trying to identify some fundamental difference between them to explain the screaming, fist-pumping, flag-waving, wig-wearing passion in the O2 arena. The differences my imaginary alien identified were purely visual and aesthetic, differences that (unless you’re the type of person who suffers from Stendhal syndrome) seem unlikely to account for such emotional investment.

I abandoned my thought experiment quickly, because the conclusion I came to (that the Federer-Nadal rivalry is meaningless without history, without context) was so unsurprising and dull. But my impression of the passion aroused by these two men and something as essentially trivial as the way they each hit a tennis ball remained. The levels of brand-name-recognition and -loyalty, and other marketing buzzwords which must make corporate executives at Nike and Armani and Netjets weep with joy, that Federer and Nadal bring with them to each tournament they play is both remarkable and reflected in the rapturous reception given to both at the O2 arena.

The actual and current world no. 1, Novak Djokovic, who entered to enthusiastic if decently-restrained applause tonight, has yet to carve out a niche for himself in the same way. In an individual sport like tennis, players are required to have the one-dimensional and larger-than-life personae of 1930s movie stars; vamps, ingénues, jokers, warriors. Tonight’s loss notwithstanding, Djokovic currently bestrides the tennis world like a colossus, but it seems as if opinion-formers and the casual public haven’t quite figured out how to categorize him. There still isn’t a hook, a keyword to define who he is and what to expect. It’s the reason why some still cling to the outdated ‘joker’ tag despite the fact that its appropriateness has faded, its applicability expired; nothing so simple has taken its place.

With Djokovic’s opponent, David Ferrer, things are less complicated. Ferrer is a fan’s player, someone whose name is not that well-known among the general public outside Spain (presumably), but who is a byword for hard work, consistency and maximizing one’s talent among tennis fans. He’s a commentator or pundit’s delight, giving them plenty of scope to coin a phrase; he’s a wall, he’s an iron man, a player who goes for jogs to cool down from a work-out. He is solid through and through, a reputation enhanced by a face which sometimes seems to be all determined jaw. And tonight, he is inspired.

In the first game of his 6-3, 6-1 victory over Djokovic, with a marathon rally which takes him to deuce on Djokovic’s serve, Ferrer announces his intentions, or rather makes it clear how much it will take to beat him. Ferrer is a break ahead before Djokovic plays his first truly dominant point, getting the jump on Ferrer for once, dominating from inside the court; but the world No. 1 does not seem motivated by the same urgency in attack as in defence. Ferrer, on the other hand, has the intensity of knowing that his hopes in this match depend upon his ability to relentlessly step up and take the ball early.

Between points, Djokovic treads slowly in a wide semicircle; preparing to receive serve, Ferrer jogs from foot to foot on the spot and his free hand flicks out, gesturing as if to accompany a silent pep talk he’s giving himself. Ferrer also has the unusual habit of carrying his towel in his mouth when he gets up from his chair, perhaps to keep his hands free for action, or perhaps simply to bite down on something. Everything about Ferrer—the towel in the mouth, the flying fringe of hair above his headband, the frantic feet, the hunched way he hits the ball as if milking every last kilojoule of energy from his body—is redolent of effort; is sincere; is earnest.

And yet his slow-and-steady reputation is at thorough odds with the almost reckless refusal to back off from taking the ball early in the teeth of Djokovic’s groundstrokes, the way he’s flinging himself behind the ball.

That word ‘inspired’ comes back to me as Ferrer hits a scorching attacking forehand to break early in the second set. It’s not a word we usually associate with Ferrer, who is—in the very, very unusual terms of being one of the absolute, global best at something—a relative mediocrity in a world in which Nadal and Federer have redefined excellence to the extent that Djokovic had to win three Slams in a year just to get into the conversation. It has always seemed to me that the best or at least the most painless way to deal with mediocrity, with being less than you might want to be, is to stop trying. This, of course, probably explains a lot about me, but more about David Ferrer.

A part of me would like to know how he does it—keeps trying, that is; keeps believing he can beat the best in the world when so often that seems not to be the case—but even if I dared to ask the question or could find a context in which it would not seem inappropriate, it’s probably one of those things. If you need to ask, you’ll never know.

As I’ve written before, when it comes to tennis players, clichés are just that for a reason; because they participate in the reality they represent. You can watch Jo-Wilfried Tsonga play a match and find that nothing comes to mind except words like flair and panache and elan; you can learn more about Janko Tipsarevic sitting in one press conference and observing the stillness of his face as he answers questions than you can in a three-set epic. Sometimes conditions aren’t right to see through or beyond a stereotype; sometimes you’re just tired and you have a cold, and it feels like there‘s nothing new and interesting to be learned.

And then sometimes, someone you’ve thought of for years as predictable surprises you, and forces you to look at them again with new eyes. Like most epiphanies, it will no doubt quickly lose its force and be forgotten. But just for tonight, dogged, stubborn David Ferrer is the most exciting man at the World Tour Finals.

Hannah Wilks is covering the World Tour Finals and is a frequent contributor to TENNIS.com.