An egregious act of sexism occurred at Wimbledon on the opening day, but there was no protest about it. It did not occur once, but multiple times.

It happened when Kiki Bertens played Petra Kvitova, when Caroline Wozniacki played Zheng Saisai, when Heather Watson played Caroline Garcia. It happened when Svetlana Kuznetsova played Laura Siegemund, Jelena Jankovic played Elena Vesnina and Teliana Pereira played Camila Giorgi.

I am talking about how women, in the second decade of the 21st Century, an age in which we are familiar with feats of endurance by females, are still asked to play tennis matches over three sets.

If you think this is a trivial issue, consider the symbolism.

Think of the girls and boys watching on television and noting that, at the precise moment when the third set is completed, at a time when male competitors would be steeling themselves for the most intense stage of the match, female players are expected to shake hands, smile and depart the stage.

Here is the question that strikes one most forcibly: Why do female players acquiesce in this sexism?

They have been vocal in calling for equal prize money, equal status, equal everything. But when it comes to playing over five sets, rather than three, what you might call equality of effort, something that these lithe and impressive athletes are perfectly capable of doing, everything seems to change.

You might almost call it hypocrisy, particularly when you factor in another aspect of "unequal treatment" - that on days when the temperature is above 30.1 deg C and where this is coupled with elevated humidity, women are permitted a 10-minute time-out between the second and third sets.

This rule was created at the behest of the Women's Tennis Association (WTA), has been adopted by the All England Club and contains a certain logic when you consider health hazards like dehydration.

But if men are expected to play through intense heat, if they manage to do so over five full sets, the extra two at least doubling the physical and mental exertion, not to mention the reduced rest time between matches implied by this, one can at least ponder why women players, and their supporters in the media, have not been complaining about yet another insinuation that they lack strength, resilience and staying power.

These regressive rule differences represent an insistent form of sexism. They reduce expectations, both of women and about women, they implicitly justify other differences in treatment well beyond sport and they serve to bake 19th-century assumptions into the waking reality of a 21st-century entertainment spectacle.

It is worth remembering that when Billie Jean King created the WTA, she did so as a conscious statement of liberation. She was outraged by the peripheral nature of women's tennis, the sense that the world existed under the assumption that strength and vitality were masculine attributes.

In many ways, it worked. Today, there are positive signs across sport inspired by King's revolution.

And this is why it is so jarring that in tennis, a sport that was once a bastion of progressive ideals, women are being demeaned by a set of rules that should have disappeared in the previous century.

But the will for change to happen is conspicuous by its absence.

It is difficult to resist the feeling that the women players are capable of talking the talk, but not walking the walk. Particularly when the temperature is above 30.1 deg C.