This is the day when Rafael Nadal had his spirit broken. As impossible a thing as you could hope to see, for Nadal has always been remarkable as the most resilient spirit in sport. But on Wednesday he was helpless. Not just beaten, but eviscerated. In the end, more or less giving up.
This was the quarter-finals of the French Open. Nadal's comparative decline - he's ranked six - meant that he had to play the world No.1, Novak Djokovic, at this early stage in the tournament. And it was too much for him.
And by losing so sadly, so comprehensively and so abjectly, Nadal showed the extraordinary vulnerability of the great champion. They just don't have the practice at losing like everybody else. They don't know what it's like to be humiliated and then come back searching for your A-game. For a great champion, defeat is curiously complete.
Defeat is part of the routine for anyone in any sport who is not to be numbered among the greatest of all time. And so when Nadal was pressed to his limits by Djokovic, he simply snapped.
He was caught in a pincer movement: Djokovic on one side, Time on the other. It's not that he's that old -- he's 29 -- but the way he plays tennis was never designed for a graceful old age. He has had a series of shattering injuries, and the general battering that he gives his body in every point -- including practice -- has cost him as he enters the endgame.
And so he was beaten in Paris. It's almost impossible to understand what Paris means to Nadal. Before Wednesday his record at Roland Garros was 70 wins and a single defeat. He has won nine of the past 10 titles. He is unquestionably the finest clay courter that ever lived.
And with 14 grand-slam singles titles altogether, he looked at one stage as if he would go past Roger Federer's total of 17. Well, you reasoned, at the very least he'll pick up another couple of titles at the French. Now, after this quite ferocious setback, you have to wonder if he's got another slam left in him.
All the same, best be careful. Writing off Rafa has been shown over the years to be a game for fools. Coming back from impossible situations is how he has made his career. His favourite way of winning a point was always to get close to losing it, running down shots others would have let go - and then hitting a winner. No player in history has been better at turning defence into attack. And on clay, no one is even close.
Nadal showed all that love of battle. At least for a while. Djokovic raced into a 4-0 lead, and that triggered one of Nadal's famous fightbacks. He drew level, he saved a series of set-points, it was all happening again, but when it came to finding the quintessential Rafa miracle -- winning the set and making his opponent doubt not only his ability but his sanity -- Nadal had nothing. Djokovic calmly finished off the set, and reeled off the next two without any dramas.
Well, there was a moment at the end of the second set when you thought that the miracle comeback might just be on again as Nadal started saving set-points again. But it was then that Djokovic showed the instinct of champions, following his serve into the net to play an extraordinary half-volley winner instead.
Djokovic completed things very tidily, winning 7-5 6-4 6-1. And the succession is now complete. Djokovic is the undisputed all-surface boss of men's tennis right now. Though you have to keep reminding yourself that this wasn't the final - he has two more matches to play.
But this devastating victory does ask certain big questions. The first is about the grand slam itself. Whether Djokovic could do what no one has done since Rod Laver and win all four big titles in one season. He's got Australia, in Paris he's slain the beast, and at Wimbledon and the US Open he'll be favourite if he stays sound.
The bigger question is about how much further he can go. He has eight slams. Right now he looks like a player with a few more in him. He will certainly be numbered among the very best ever to play the game.
He's as near to perfection as you can get on a tennis court. Not in the sense of playing perfect points, like Federer, or unleashing that impossible forehand, like Nadal. But look for a weakness. Or rather, don't bother. He just hasn't got one.
He may not have a single shot that's a ten out of ten, but he has no threes and fours. It's a row of eights and nines. And when you add that to his fitness, his capacity for work and self-improvement, and now throw in the glorious extra confidence he will take from marmalising Nadal on his favourite court in all the world, you have a player who is not only No.1 in the world but also improving.
This is modern tennis, in which fitness matter, in which power matters, in which depth of shot matters. Djokovic is a player of his time - perhaps the ultimate player of the 21st century, with gym-work and diet and a crash-hot team.
But so much of tennis comes down to the same old question of dominance hierarchy: do I defer to him? Or does he defer to me? Last year I watched Djokovic attempt to beat Nadal on the same court, and it was close -- but in the end Nadal pulled rank on him and despite the score, it wasn't close at all.
But now things have changed. Nadal now defers to Djokovic. Even in Paris. The old order changeth, giving place to new. And it changeth at five o'clock this afternoon.