Sloane Stephens will play Venus Williams in a U.S. Open semifinal on Thursday. (Adam Hunger/Associated Press)

She finished sixth in the country in the backstroke and swam to all-American honors at Boston University in the same time frame when, in April 1987, Los Angeles Dodgers executive Al Campanis went on Ted Koppel’s “Nightline” to state, among other lunacies, that black people were “not good swimmers” because “they don’t have the buoyancy.”

She cringed when teammates made offhand, opposite comments such as, “You’re a natural athlete. Of course you’re going to be a good swimmer,” and, “You’re so lucky you don’t have to work that hard.”

To the Boston Herald in 1988, she said, “I’ve been the only black female at the U.S. nationals for the last five years. I was the only black female in the NCAA championships my whole career. It seems I’ve always been the only black swimmer. I’m grown up to accept it, deal with it.”

Few among the 23,000 Thursday night in Arthur Ashe Stadium would be able to behold the evening so keenly as the woman who figures to take her seat in the Friends Box. Not only does Sybil Smith figure to watch her daughter, 24-year-old Sloane Stephens, oppose Venus Williams in an all-American, all-African American U.S. Open women’s semifinal, but the other semifinal will feature Madison Keys, the 22-year-old, onrushing daughter of a white mother and African American father.

Keys, who blew through Kaia Kanepi of Estonia on Wednesday night, 6-3, 6-3, will play Coco Vandeweghe, yet another American, who always looked the more forceful player on Wednesday afternoon while upending top-ranked Karolina Pliskova, 7-6 (7-4), 6-3. Here come the first four-American women’s semifinals since 1981 and Martina Navratilova, Chris Evert, Tracy Austin and Barbara Potter, and here comes another milestone of diversification.

“Oh,” host Koppel replied to Campanis on-air that night back in 1987. “I don’t — I don’t — it may just be that they don’t have access to all the country clubs and the pools.”

The tennis testament to Koppel’s point — these U.S. Open women’s semifinals — will come on some heady anniversaries. The 2017 U.S. Open marks 20 years since Williams debuted at 17 in those famous hair beads and toiled all the way to the final against Martina Hingis. It marks 60 since Althea Gibson won Wimbledon. And it marks almost 30 since two early pioneers, Lori McNeil and Zina Garrison, reached the semifinals here, McNeil in 1988 to tussle for three sets with Steffi Graf and Garrison in 1989 by ending the career of Evert in the quarterfinals, after which Garrison wept for Evert as they embraced and Evert said, “Congratulations. You played well.”

In a sport similar to her mother’s in its 20th-century legacy of exclusion toward people of color, Stephens said, “It’s great for American tennis. It’s great for African American women. I hope that we keep it going. Yeah, there is not really much to say other than it’s amazing.”

Furthering the keen, knowledgeable eyes, there will be Geneen McCauley, a database manager for the City University of New York, an African American and a tennis fan of uncommon knowledge and devotion. (Yes, she sits up through wee hours watching the Australian Open in January.) McCauley reached the grounds Wednesday, as she does chronically every U.S. Open, with her mother, Joan McCauley. Joan McCauley told of how her daughter was an epitome of how things can and do change.

“One day,” decades ago at their home in the Bronx, “she’s sitting there, and I’m like, ‘What are you watching?’ ” Joan McCauley said.

“Tennis,” Geneen McCauley said.

And then . . .

“And then one day she calls me up,” Joan McCauley said, “and she says, ‘You know, Mom, I’m at the U.S. Open.’ I’m like, ’Where are you?’ She just came alone. Didn’t wait for her friends to tag along with her. To get a phone call, and now I’m going to date myself because when she mentioned that, I realized exactly where she was. I mean, I knew where this place was.

“But see, that world sphere over there was for the World’s Fair [in 1964] that I ended up sneaking away from my high school and my Mom didn’t know I was here, so I had to go home and I didn’t get home on time for curfew because of where I was. So when she called and said the same thing, ‘Mom, I’m here,’ kind of a flashback. So I did something that my Mom didn’t want me to do, the World’s Fair, and I would not have suggested she come out here by herself, and we both did something separately, independently, not worrying about other kids, just go for it. And that’s what kids have to do: Go for your passion. Go for what you like.”

That rang with the words of Stephens, who told of growing up across the street from Sierra Sport and Racquet Club in Fresno, Calif., playing in summer camps and, “I thought it was fun. My stepdad used to take me. That’s how I started playing.”

As Geneen McCauley watches such moments — Stephens played Serena Williams in the 2013 Australian Open quarterfinals, and Keys did likewise in the 2015 Australian Open semifinals — she reports a two-pronged thought process. Yes, she spots the significance. She hates that “the history books often bypass” McNeil and Garrison, the 1990 Wimbledon finalist, and MaliVai Washington, the 1996 Wimbledon finalist. She loves the Williams sisters but credits them with furthering what had come before and of changing the “physicality” of the sport.

At the same time, she started watching Boris Becker and Ivan Lendl, and her first undiluted tennis love was Roger Federer.

“I do feel something,” she said, “but I think what I feel is different from what the masses would feel. I’m able to look at them as individual, exceptional players, without the asterisk of saying ‘African American,’ because that’s really what they want to be known as — as athletes, not ‘African American athletes.’ And so I think any win they have should be a win because of their merit. So culturally I’m looking at it two different ways.”

At the same time, she said, “I want people to take a moment and see that each one got here in a different path. Each path is dramatically different from the other. And I think people should take note, and I’ll say this however controversial it may sound: When an athlete is different than the masses, it’s all ‘Sis-boom-bah, U-S-A, U-S-A,’ but when the cameras are turned off, perfect example, Indian Wells [and the controversy with the crowd’s treatment of the Williamses there in 2001]. So it’s like, okay, so now you see those three [in the 2017 semifinals]. Are you with those three because they’re ‘U-S-A?’ Or are you with those three because they’re the best and fought the hardest to get there?”

That question could have gone to thousands Tuesday when the crowds boomed for Stephens and Williams in their stirring quarterfinals. After the former match, the elegant Smith headed haltingly up the stairs toward the concourse. Groups of fans kept asking her for selfies. She kept stopping to oblige. Her smile radiated. Her daughter was healthy after foot surgery last winter, grateful for that and into the semifinal.

“It’s a beautiful thing,” Smith said.