by Hannah Wilks, TW Contributing Writer

Sometimes you expect much more from a match than it delivers. This has been the case a lot this week, whether because of the weaknesses and flaws inherent in the round robin format or because sometimes it just happens that way. The strength of the ATP is so concentrated in its elite players that even among the top eight, a natural division has quickly emerged between the best and the rest. Three semi-finalists have already been settled, with the fourth to be determined by tonight's clash.

Surely this one won't disappoint. Two players from whom one never knows quite what to expect; Novak Djokovic, an unpredictable firecracker, prone to lapses of concentration and bizarre physical reversals, and Roddick, the workhorse who can be relied upon to give his all, but whose game can run the gamut from almost unbeatable to ineffectual.

Their head-to-head is 5-2 in Roddick's favour, which in theory looks one-sided, but most of those wins have come for the American during Djokovic's prolonged slump. I understand it's strange to use the word to describe the progress of a consistent trophy-lifter who has been, during his 'decline', as high as no. 2 in the world. But since Wimbledon 2008, Djokovic's game has touched for periods on every variant of toothless. His serve has been broken down and rebuilt, he's visibly struggled for confidence. He's often looked like a shadow of the cocky upstart who barged on to a world stage dominated by Federer and Nadal and demanded that they yield the floor.

But all of that has seemed like ancient history since Djokovic's September resurgence in New York, wher he defeated Federer and stretched Nadal in the final of the US Open. Surely this time he can take it to Roddick.

An extra frisson is added by the fact that at times these two don't seem to like each other very much. Whatever latent animosity exist came to the fore following Djokovic's last victory over Roddick at the 2008 US Open, when the Serb's attempts to retaliate against Roddick's mockery saw him booed by the New York crowds. That the spat was public seems inevitable, as both have well-deserved reputations for being entertainers, earned with Djokovic's impersonations and willingness to make fun of himself, Andy Roddick's sardonic wit in press conferences and on chat shows. They're frequently referred to as 'characters', actively seeking to be larger than life.

One thing that doesn't disappoint is Djokovic's entrance. Aware of the fact that the abiding impression he has made this week came when contact lens problems derailed what promised to be a classic encounter with Nadal, he takes the court accessorizing his grave expression with a rakish black eye patch. Solemnly letting the small mascot lead him to his chair, he fits the eyepatch on to her head and sends her on her way. It's possible to read the stunt as a plea for affection, but the twitch of his lips, betraying his own enjoyment, suggests that in the final analysis he did it because he knew he would relish the joke more than anyone. It's a generous piece of slapstick, and the crowd love it. It's hard to imagine Roddick doing the same thing.

There's an odd, tense atmosphere. The crowd are more well-oiled than usual, enthusiastic but ragged, with no consensus favorite. Someone yells out during Djokovic's service motion and is roundly tutted for his pains. On the evidence of the first few games, it's going to be a proper tussle - maybe not in terms of quality of tennis, but it promises to be a prolonged bout of psychological grappling. Roddick pushes from the baseline, mixing up spins and pace, giving the Serb all the rope he needs to hang himself. It works; the rallies end more often than not with an error from Djokovic. Seduced into these circuitous exchanges, Djokovic's aggressive instincts seem to desert him. It's puzzling;  how can Djokovic be out-defended when he's so much better at it? The simple answer is that Roddick seems to bring out the worst in Djokovic.

But Djokovic has come a long way. He rapidly gathers himself and finds purpose and aggression. As soon as he starts hitting forehands moving forward into the court, everything is different. You expect Roddick to hold his ground, but as soon as he meets with resistance, he crumbles, giving up the first service break with a backhand slice that drifts wide. He holds the next game, but cannot find the wherewithal to finish points. At one point, he was obliged to wait for Djokovic's third defensive, desperate lob to get the miss. Roddick gives up the set - and I do mean gives up - with another unforced error long over the baseline, and we plunge deep into the realms of the anti-climactic.

Djokovic has qualified for the semi-finals, and he knows it. All that is left on the line for the American is pride. It seems like that should be enough, but he still cannot capitalise on the momentary lack of attention with which Djokovic starts the second set. In fact, it's the American who is lacking in intensity. The usual audible heavy breathing, the huffing and puffing like a steam engine which seems to get him around the court, is absent. After a failed Hawkeye challenge, Roddick stares at the umpire with obvious displeasure. The crowd cheers, hoping for Roddick to shed his patience and get fired up. But his unbelievably passive play continues. Roddick has had his health issues this year, but this seems almost a trend, and it's worrying. How can such an energetic and forceful person play so timidly?

One could also ask how someone as complex as Djokovic, with all the faults and fissures of his past, can play a game so miraculously smooth? I could watch him hit all night, not that Roddick seems likely to enable it. I've been searching for an image that describes the flight of his groundstrokes, when it comes to me; the limpid parabola of a stone skimmed across water. There's so much talent evident in every stroke. It's exciting to watch, simply because we don't know yet how his week, his year, his career, will turn out.

Roddick, it is plain, has no surprises left. He makes a gallant last stand to hold his final service game, but succumbs on yet another unforced error long over the baseline. He leaves London with no wins, but the crowd cheer him out of the arena with an affection that clearly demonstrates that Roddick is best-liked these days as a plucky loser.

Djokovic stays to chat, joking with the crowd, friendly and adrenaline-drunk. He's twenty-three years old and has proved he has the ability to stay in the mix; he has unnumbered chances left to shape the rest of his story. Roddick's opportunities are growing few and far between; his time in London has already run out.