Ashleigh Johnson is the first African American to play on the U.S. women’s water polo Olympic team. (Jonathan Newton/The Washington Post)

Under a different set of circumstances — say, for instance, if Ashleigh Johnson hadn’t hated swimming with every fiber of her being, or if her mother hadn’t finally given in to her pleading to let her quit after her sophomore year of high school — Johnson and Simone Manuel might have made history together at the Olympic Aquatics Stadium at the 2016 Rio de Janeiro Olympics. Instead, they are making it separately.

In the same pool where last week Manuel, a U.S. sprint freestyler, became the first African American woman to win a gold medal in an individual swimming event, Johnson, a goalkeeper who is the first African American to suit up for the U.S. women’s Olympic water polo team, on Monday led the defending champions into the semifinals. With Johnson pitching a shutout for her three quarters in goal, the U.S. throttled Brazil, 13-3, setting up a matchup Wednesday against Hungary, the winner of which will play for the gold medal Friday.

With the Aquatics Stadium converted from swimming to water polo, Johnson, who turns 22 next month, found herself bobbing in the middle of a pool — now festooned with nets and shot-clocks — at right about the spot where Manuel crossed once in winning silver in the 50-meter freestyle and twice in winning gold in the 100.

While the lane lines from swimming were gone, the starting blocks remained in place — and Johnson was tempted to get up on them and race a 50 free exactly . . . never.

“Not. At. All,” she said. “Those days are gone.”

The world will never know what would have happened had Johnson, a former Florida Class 1A state champion in the 50-yard freestyle, stuck with the sport. But Andy De Angulo, the swim coach at Ransom Everglades School in Miami, has a pretty good idea.

“Put plainly,” De Angulo said by telephone, “instead of everybody talking about Simone Manuel at this Olympics, we would be talking about Ashleigh as well. She would have been a superstar.”

Race results on USA Swimming’s website, while perhaps not exactly proving De Angulo’s claim, at least hint at Johnson’s potential. Her 50 free time at that state championship meet in 2009, when she was 15 years old, was 23.46 seconds — which put her in the top 10 of 15-year-olds nationally. Two years later, Manuel’s best time as a 15-year-old was 23.33.

But Johnson hated swimming. “We had to drag her to practice,” her mother, Donna, said Monday. Ashleigh would do things like “forget” her swimsuit or goggles at home, until her swim coach finally figured out to bring extras to practice. When Donna finally let her quit swimming after that 2009 state championship, Ashleigh’s only regret, her mother said, “was that she had to swim at all.” That 50 free at states was the last competitive swim of her life.

“She didn’t mind the work,” De Angulo said. “Most kids walk away because it’s boring and hard. Ashleigh was the opposite. She didn’t like the meets. She wanted to feel like she was more part of a team.”

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She found that dynamic in water polo, which her high school also offered. She and her younger sister, Chelsea, a center, joined the girls’ team, and eventually both wound up at Princeton. Donna still remembers the first time the girls went away to a large statewide tournament in Florida.

“They came back home and said, ‘Mommy, those girls on the other team were trying to kill us! They were trying to drown us!’ ” Donna Johnson said. “I go to the coach and I say, ‘My girls said the other girls were trying to drown them.’ She just says, ‘Mrs. Johnson, that’s water polo.’ ”

Though the nature of her position allows Ashleigh Johnson to stay mostly out of the worst of the below-water violence that goes on in water polo — in which players essentially attempt to drown, injure or denude each other at any opportunity — her athleticism and physicality (she stands 6 feet 1) are on constant display. She bobs around with little more than her head showing, but when an opponent takes a shot, suddenly she rises in the water almost to her waist, as if walking up a staircase, and whips her long arms to swat away the ball.

Like Manuel in swimming, Johnson hopes her success inspires other African Americans to take up her sport.

“I want people to look at me,” she said, “and see how much opportunity there is and how far they can go.”

And while she would never try to talk someone out of swimming, she also doesn’t hesitate to point out the difference, as she sees it, between that sport and the one she chose:

“Water polo,” she said, “is fun.”