INDIAN WELLS, Calif. — It has been more than 20 years since Venus and Serena Williams first reluctantly faced each other on tour, the unavoidable result of their father’s far-fetched but ultimately successful plan for both of them to reach the top.

Across the decades, sport’s first sisters have dueled through their mixed emotions on four continents and in the finals of all four Grand Slam tournaments. They have played in brilliant sunshine and under closed roofs. They have played on grass, on red and green clay and on hard courts of varying speeds.

But there has never been an all-Williams occasion quite like Monday night’s in the third round of the BNP Paribas Open, in which Venus put an end to Serena’s comeback tournament from maternity leave with a 6-3, 6-4 victory.

It was odd enough to see them playing in the third round at all. This was their earliest meeting in a regular tour event since their first professional encounter in the second round of the 1998 Australian Open, during the beads-and-braces phase of their teenage years.