LONDON—A Simon & Garfunkel song comes up on my mental jukebox as I return to the O2 Arena a year after I left: Hello darkness, my old friend … The crowd here in the upper levels are kept in darkness (except when roving spotlights polka-dot the audience after a winner) during the match. Although it lacks the immediacy of being out in the elements, indoor tennis and this event in particular has a vibe all its own. You feel safe, cocooned in unseasonable warmth, shrouded in darkness.

The court is a floating island of blue light in the midst of the dark arena, saturated in radiance. It’s easy to let your eyes become flooded and your aliveness to what happens on the court be dulled, lulled into a zen state where the flight of the ball becomes no more than an abstract curiosity.

That’s how it feels when Roger Federer plays his first match on Sunday against Jo-Wilfried Tsonga, a three-set encounter that never truly seems in doubt. Federer matches the soft blues and purples of the court, but Tsonga’s red shoes catch the eye and draw attention to his feet, which seem in the first set to be stuck in the mud. He may want to click his heels together three times and think wistfully that there’s no place like Paris, but he didn’t have much luck there either. When Tsonga gives up his first break, Federer hasn’t done much, really. He plays one truly excellent point, placing an expertly-judged thumb on the scales. The margins are so thin that it’s all it takes.

TV has taught me that it takes less than a pound of pressure to pierce human skin, that we are fragile creatures. I don’t know how you translate mentality, ambience, and the intangibles into pounds and ounces, but nobody is immune from their weight, as Federer’s drop in play in the second set shows. It releases Tsonga from his shackles, though, gets his feet moving. It’s not a coincidence that Tsonga’s best moments in this match came when he softened his usual blistering, bludgeoning arsenal with delicate, feathery slices and soft touches at the net. A reminder that he is so much more than the bruiser he is often made out to be; a further frustration.

I’m sorry when the match ends, not with a bang but a whimper. I had so many more jokes about Tsonga’s shoes.

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Whatever stage-fright or lingering sleepiness afflicted Tsonga in his first set against Federer, Mardy Fish seems to have it too. It is stunning to watch Rafael Nadal indoors; an intimidating prospect for a debutante. It’s hard to say whether he is making the surface look good or vice versa, but the court seems to work for him and the work he gets on the ball. It sometimes seems to travel across the net surprisingly slowly given the visible and audible effort that’s gone into the strike, but once it hits the court it uncoils and rears up, so that it ricochets off Fish’s racquet in unpredictable ways.

Against all of that, Fish just looks like a featherweight from the baseline. But somehow, by the time we’re a few games in the second, Nadal is playing so far back behind the baseline in that empty blue space that the court itself seems to elongate; he has to be dragged inside the baseline by a Fish drop shot. Suddenly Fish has wide swathes of space to play with and he isn’t slow to accept the invitation. He seems to have come to terms with the way Nadal’s ball behaves; from seeming like a lightweight, he’s now sleek, silky, deadly.

As they trade breaks in the third, the atmosphere in the arena changes. It could be just the tense silence of thousands of people trying to find out when the last tube goes and doing travel calculations on their smartphones, but although this is not necessarily the highest-quality tennis, it’s not soporific and nobody’s sleepy. It’s electric. At various points during the third set, couples torn between staying and leaving perch on the edge of seats near me, trying to take in a last couple of games. A middle-aged, jowly man who looks like a cabbie has his head in his hands and seems to be praying under his breath, before roaring when Nadal holds serve; a woman with long beaded braids takes his seat after he leaves and screams the most English-accented ‘VAMOS!’ I’ve ever heard. These are probably not people who engage in the Wittgensteinian language-games of the blogosphere. But they’re here in North Greenwich on a Sunday night, risking the night bus to live and die with every point.

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I don’t know why I spend so much of my life defending Andy Murray, or at least trying to explain why I like him. But wherever I’ve been in the past few days—talking to friends, or other fans, or strangers in the bus queue, or the O2 catering staff person with a tray of burger buns in the elevator—the conversation seems to come back to that.

Monday’s performance won’t make that conversation any more fun. But there’s still moments of brilliance, moments that make me shake my head and roll my eyes, torn between appreciation and exasperation that he has to make it so hard for himself. Early in the second set, mired in probable defeat, he makes a small ‘oh’ of disappointment in the middle of a rally he seems to be dominating; two shots later, he lands a forehand in the net. Later, he loses the match on a point where he decidedly attempts to be too cute. On the other hand, he pulls off passing shots, slices and offbeat flicks that no other member of the Top 5 would attempt or could pull off with such casual style. It’s as if all the personality suppressed by his dour demeanour finds expression in the sometimes mad-scientist creativity of his tennis.

Murray is sometimes called a reactive player. Intended as a dismissive comment on his perceived passivity, watching him explode across the court to chase down a drop-shot or improvise something out of nothing makes me think instead of chemicals, reagents. Like oxygen, which interacts with its environment in a variety of ways—fire, rust, life—Murray can be the catalyst which ignites a crowd, or dampens our enthusiasm unexpectedly. Whether it’s him or the Monday afternoon of it all that keeps the decent but not capacity crowd depressed, it’s hard to tell, but the atmosphere is not electric.

Nevertheless, when he is lying down between sets having treatment and the very real possibility of a serious injury is before us, all the air seems to go out of the arena, and the tournament.

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