They didn't make it Williams day here yesterday, not officially, but they might well have done. It always is, anyway, when Venus and Serena are in good health and good form and devoting a little time to the game they play on a different level to everyone else. On cue, the rest of women's tennis falls back in the panic of a retreating army.
In truth it's not much of an army, we were reminded again when the sisters moved into the semi-finals.
Minus the Williams girls it would, frankly, be a travesty of the game which used to boast players of the quality of Martina Navratilova, Chris Evert and Steffi Graf.
A tournament official rather confirmed this at the weekend when he said, in so many words, that in lieu of significant women players and significant matches the Centre Court would be titillated by some of the more glamourous occupants of the locker room. Or, it might have been said, never mind the backhand dear, take another inch off that skirt.
Then there are the Williams girls. Yesterday Venus, who is going for her sixth Wimbledon title, swamped Polish starlet Agnieszka Radwanska, a 20-year-old from Krakow, 6-1, 6-2 in one hour, eight minutes on Court One. Serena was almost as brutal, beating the high-spirited Belarusian Victoria Azarenka on the Centre Court 6-2, 6-3, taking just five minutes longer than her sister.
Both the vanquished admitted they had been facing unbeatable forces.
Radwanska, who had the demeanour of a road-crash victim on those many occasions when Venus swooped on the ball with whoops of ferocious concentration, declared: "It can be the same final as last year for sure – Venus against Serena, both are playing so well.
"It was impossible for me today, everything she hit seemed to be in and hit so very hard ... then there is the serve, 120mph, it's tough. I was trying so hard but I couldn't do anything. I did a little better in the second set, I try to mix things up a little bit, but it was no good – when you play Venus or Serena it is not the same as meeting other opponents."
Azarenka, notably not for turning or intimidating – she booed the crowd at Roland Garros in the French Open when they booed her for competitive grunting – offered a little resistance in her second set with Serena but soon enough subsided under the weight of some stunning ground strokes. She said: "The Williams sisters are playing so well they deserve to reach the final. I'm not going to talk about whether it is they who are so good and the rest not so good, because I don't think that is fair, but it is definitely different playing them.
"Today I did everything I could but I knew it was difficult because I was playing the unbeatable Serena. She played amazing tennis. Just when you though you had a chance, she did something that you couldn't respond to. Everything about her is strong on the court. Yes, she has everything, she is the complete player.
"She has every shot. She's very strong mentally. She fights until the last minute. What can you do? It's a pretty strong package, you know."
Strong enough, in most minds indeed, to make all competition here seem marginal when it does not involve Venus beating Serena, or Serena beating Venus.
Serena said she had an additional force in beating Azarenka with the need to avenge defeat in Miami earlier this year. "You know, I really wanted to show up today, and when she started to do well in the second second, I just told myself that this wasn't good enough, I wasn't serving well enough, and I just had to do something about it.
"I wouldn't say anything about Venus and me being better than all the others. All I would say is that the Williams' game has got some very strong points and I feel blessed that I have had my dad to coach me.
"If we have any advantages it is only that both of us work very hard."
It doesn't sound much, working hard – everybody does that – but when you listen to the Williams girls you cannot fail to notice in amid the work ethic and the ambition, there is also more than a touch of a powerful mystique. Their opponents feel it – and so do they.
Venus was asked if she felt invincible and intriguingly she did not return the service. "You know," she said, "I do a lot of things right. You know the first set today was really almost perfect. Do I feel invincible? I'd like to say yes, but I really do work at it."
She was also asked how she would feel if she had to play herself. "I guess it would be the same way I feel when I have to play Serena. One thing for sure, you cannot give an inch. You have to be on your best game, you know that when you play Serena."
It's a family product of course, a ferocious combination of selective dedication – there are times when they would rather hang around with their Hollywood friends – and belief that if you're going to play tennis you better be in the best possible condition.
Yesterday that way of thinking and acting carried the Williams girls, once again, on to another level from all who are supposed to give them a game. Yes, it was Williams Day at Wimbledon yesterday. For the foreseeable future, it always will be.