Maybe it was that he lost his first set of the tournament or the creeping derision over his unfolding career as a fashion model or the tensions that can come with impending fatherhood. But there it was, plain as his native Alps, Roger Federer wasn't quite his recent self yesterday.
This is to say there were moments when he looked something less than the greatest tennis player the world has ever seen.
He was still a beautiful one most of the time, of course, a purveyor of some shot-making which continued to defy belief, but after the first tide laden with this bounty had swept over the Centre Court there was a remarkable sight.
It was of Philipp Kohlschreiber, ranked 32 in the world, still standing on his feet and still, apparently, ignoring that classic advice once given to an overmatched fighter.
The cornerman looked across the ring to Mike Tyson, groaned inwardly, and said, "Make sure you don't land a real punch, that might really piss him off."
Kohlschreiber probably knew that it wasn't wise to similarly incite Federer, especially when, you had to suspect, he was anxious to impress on his audience that whatever Andrew Murray, his most serious challenger here in the absence of Rafael Nadal, could do he could do rather better. That seemed a distinct possibly when Federer ripped two aces past the 25-year-old German in the first game, one won in less than a minute, and threatened to maintain a constant level of such superiority before sliding into something close to a heap of indecision in the third set – one he was apparently controlling as effortlessly as he had the first two. It was at this point, with Kohlschreiber playing shots of extraordinary boldness and Federer's shot selection suddenly becoming somewhat less convincing evidence of natural-born genius, that Murray's progress in the other half of the draw suddenly began to look rather sweetly grooved indeed.
While Murray was imperious in beating the Latvian maverick Ernests Gulbis the night before, Federer had to make a serious self-examination after losing a third-set tie-break 7-5 and, in terms of confidence and nerve, a rather greater margin than that. As it emerged Kohlschreiber had indeed provoked the kind of reaction feared by that old, worldly-wise boxing trainer, Federer served the first game of the fourth set with such ferocity that you had the overwhelming impression that it was very much the brisk beginning of the end of the battle.
That belief was confirmed in the next game, when Kohlschreiber could only have surrendered his serve more pitifully if he had fallen to his knees and wept. This was a pity because the man beaten 6-3, 6-2, 6-7, 6-1 who includes among his recent victims the world No 4 Novak Djokovic, had earlier done something beyond the powers of the vast majority of the world's tennis players.
He made Federer look distinctly vulnerable, at times playing tennis of quite breathtaking adventure and qualifies as one of this tournament's prime victims of a misleading scoreline. Federer was, no doubt, always the likely winner but he has rarely needed to be more forcefully brought to attention. Kohlschreiber achieved this with the sheer quality of his play, and it was something Federer admitted even as he rather tetchily fended off questions about the nature of the Murray performance on Thursday, "I didn't see that match," said Federer, sharply enough, and a little later snapped that talking about a Federer-Murray final was "premature". In fact there had to be a sharp suspicion that Murray's growing aura might just be having a little effect on the psyche of the master player.
Certainly he was keen to stress the positive sides of his performance, of which there were undoubtedly many. Federer said: "I thought it was my best match of the season. I thought the rhythm was very high. We played a lot of tough points. I really thought that from my side it was an excellent match. Of course you also need your opponent to come up with the goods to make it an exciting match and I thought it was. Sure, I would have liked to win it straight, but he came back strong.
"Maybe my serve let go just a little bit. But he started to pick a side a lot as well and took the right decisions at the right time and in the end he deserved the third set.
"I was happy the way I reacted. Sure it was a good test, and why not? I mean, I thought I already played well for the first two matches – you know it doesn't really bother me how I come through. The important thing is to get through and then feel good when you leave the court."
Federer, it has to be said, had moments which cannot have thrilled him as he contemplated a re-match with Robin Soderling, the highly committed Swede who will be anxious to do better on grass than he did on the red clay of Paris in the final which drew Federer to the brink of a record total of 15 Grand Slam triumphs.
Kohlschreiber was philosophical enough after establishing that he had the talent to duel, at least for a little while, with the man who has set the best standards of the game.
"It's always pressure against him," Kohlschreiber said , "he starts so easy and smooth and you think hell, this is going to be tough. But then it's always nice to play against him. He's a funny boy and I like it when he is on the other side of the net. He makes you play as well as you can. Unfortunately, you know that most of the time you gonna lose."
This is especially true, as the old boxing man was saying to his charge, if you have the temerity to try to do some hurting yourself. That Kohlschreiber did this to a considerable degree was clear enough on the face of Roger Federer – not to mention his ruinous reaction to the sound of the last-round bell.