LONDON—This is a strange tournament. For the first few days, you feel as if you’re stuck in some sort of tennis-specific Groundhog Day, watching the same players play each other over and over again for rewards or avoiding penalties that aren’t precisely clear. Then suddenly it’s Saturday, we’ve got rid of half the field, and the four players that are left are trembling on the edge of elimination in a very final and familiar way.

It’s a strange tournament, but not by any means a superfluous or less-than-valid one. I know there are healthy doses of scepticism in some quarters regarding the whole concept of a season-ending championship, and no doubt it’s far from perfect, but every player this week has competed with as much intensity as they are capable of. Some have had less to give than others, but everybody is exhausted at the end of a long season, as David Ferrer reminded us when told he didn’t look as tired as other players this week: “But I am tired. I am tired, sure. I’m very tired. Me, I was fight[ing]. But I’m very tired. I want to stop, but I can’t because I have the Davis Cup. But I’m really tired.”

Translation: He’s tired.

I can see why the question was asked, because Ferrer has seemed as much a ball of relentless energy as ever on the court this week. But fatigue manifests itself in different ways. If this afternoon’s match between Ferrer and Roger Federer had been played earlier in the year, it would be hard to imagine that Ferrer wouldn’t sink his teeth in when the champion briefly exposed his jugular in a five-deuce, eight-minute struggle to hold serve at 4-5, or at least force Federer to come up with something rather than letting him off the hook with consecutive backhand errors.

Ferrer, of course, was fighting history as much his opponent—his own personal 0-for-11 history against Federer; the glittering, magnetic prospect of a monumental 100th final, possible 70th title and sixth season-ending championship for Federer. I liked Federer’s response when asked to put himself in the mental shoes of Ferrer, taking the court against an opponent who has beaten him 11 times: “It’s up to me to remind him of that record. … It gives me a sense of security to some degree, but not him. I don’t think it scares him in any way.” Ferrer certainly didn’t play scared today; not his best, but not scared. If anything, the history seemed to weigh on Federer’s mind more, if his poor beginning and persistent carelessness throughout the match—I am thinking particularly of the point for 1-2, second set, when Federer failed three times to put the ball away, allowing Ferrer to play an admittedly spectacular reactive point—are any indication. Maybe that security Federer referred to elides easily into over-confidence or complacency, or perhaps he is as mentally tired as everyone else; it’s only really one match out of four that he has played with no lapses in intensity or focus, but in that one (vs. Nadal) he was relentless.

He will need to be relentless again on Sunday, because his opponent will be Jo-Wilfried Tsonga, proof enough that this tournament can also produce strange patterns, like the mirror-image scores each won by today—7-5 6-3 v. Ferrer; 6-3, 7-5 v. Berdych. This will be Federer and Tsonga’s eighth meeting in 2011, and the final three of that eight have taken place on three consecutive Sundays: the final of the Paris Masters, which Federer won in three sets; the first Sunday of this tournament, in the round-robin stages, which Federer won in three sets; and now another final. The pattern may not be promising, but Tsonga was cheerful when asked what he expected to happen tomorrow: “You know what I expect. I expect to win, of course.” He smiled widely, mutely inviting everyone to join in. “I will give everything. If I have to break my two ankle [sic] to win, I will do it for sure.”

Giddy with apparent relief at winning a match that by his own admission he did not play well, Tsonga turned questions about his coaching situation into jokes“I’m just by my own and that’s enough. Sometimes we are two or three in my head, you know, so it’s enough.”—but the tone turns somber for a moment when he is asked what he did to beat Federer at Wimbledon and in Montreal which he hasn’t managed to do since. “Maybe I was physically, you know, better,” he muses. “But I really don’t know. Sometimes it depends a lot of the level of Roger. If he’s playing well, you know … it’s difficult …”

His voice trails into silence and there’s a moment where everyone quietly acknowledges the understatement.

The match-up is already spawning portmanteaux like nobody’s business (my favourite is Fedonga) and with the tournament having failed so far to produce a real high-quality, dramatic classic match, expectations are high. Both of these men obviously have it in them to thrill the crowd; they don’t coo with appreciation for Tsonga as they do for Federer, but are more likely to respond to one of his mammoth shots with a half-grunt, half-sigh as if they have just taken the full force of that strike in the gut. Unlike Berdych, who often can appear like a windmill of elbows and knees out of which the ball flies randomly, Tsonga is also a smooth, fluid mover when he gets going, and the serve-and-volley picked up off his toes he produced for match point tonight was nothing but pure skill. He could be great.

Federer stands overall at 6-3 in the head-to-head. Yet among those six victories for Tsonga was the Wimbledon quarterfinal this year, and it‘s my personal (and thoroughly unscientific) opinion that if there is one match that got away in 2011 that Federer would want to have back, it was that one. Neither man played well in the semifinals. Maybe they’re saving it all for the very last match of the season. It could be great.

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