NEW YORK — Any potential museum of sports parity should include, in its symmetrical building, a front-room exhibit on women’s tennis in 2019. Not only has the sport managed to yield three different Grand Slam champions and six different Grand Slam finalists, somehow it has had 12 different Grand Slam semifinalists.

That has happened only one other time in the Open era (2004), and if women’s tennis could forge a plausible U.S. Open final foursome of, say, 15th-ranked Bianca Andreescu, No. 13 Aryna Sabalenka, No. 11 Anastasija Sevastova and No. 9 Madison Keys, none of whom has reached a Grand Slam semifinal this year, that would bring parity paradise.

Often, people arrive at sporting events hearing the farcical assessment that anybody can win.

Here, it might even be true.

“Everyone can win any tournament, even the Grand Slams,” said Simona Halep, the 2019 Wimbledon champion whose first-round match with No. 135 Nicole Gibbs went three sets, an everyday complication of a sport in which the No. 135 player is so much better than the No. 135 player of, say, 10 years ago.

The final Grand Slam of the 2010s barely had begun when some bright lights met with the familiar switch-offs of parity central. No. 14 Angelique Kerber, reliable winner of three Grand Slams in 2016 and 2018, left right away Monday, falling to No. 54 Kristina Mladenovic, 7-5, 0-6, 6-4.

No. 25 Garbine Muguruza, winner of Grand Slams in 2016 (French Open) and 2017 (Wimbledon), left Tuesday, having run across No. 36 Alison Riske of the United States, stormed through the first set and lost 2-6, 6-1, 6-3.

No. 10 Sloane Stephens, the 2017 champion here, recently switched coaches back to her coach of 2017, then found herself in Arthur Ashe Stadium on Tuesday night against No. 127 Anna Kalinskaya of Russia, then found herself exiting via a 6-3, 6-4 route 84 minutes later.

Even Serena Williams, who doesn’t dabble much in early-round drama, had a turbulent go on Wednesday night against 17-year-old Catherine McNally from Cincinnati, having to rummage around for her inner Serena to deliver a 5-7, 6-3, 6-1 win.

Eccentrically enough, a sport with 12 women taking 12 semifinal slots across three Grand Slams operates alongside a men’s tour that could not contrast more. No. 1 Novak Djokovic, No. 2 Rafael Nadal and No. 3 Roger Federer cruise through draws with such regularity that if Federer loses a set to India’s impressive Sumit Nagal in his opener Monday night and another set Wednesday to the commendable Damir Dzumhur, it qualifies as interesting. Only seven men have reached Grand Slam semifinals this year amid the deathless big-three hegemony.

In the 2010s, six men — six! — have shared the 39 Slams, with but seven more men managing to become beaten finalists. The women’s numbers there are 18 and 13, striking given that the sport very much has included the Serena Williams dynasty (12 titles in this decade). Without Williams, the hodgepodge would be even more a hodgepodge.

Riske, 29, and Muguruza, 25, played each other Tuesday, then spoke similarly of the overriding factor: a deepening depth. It seems the planet continues to produce more humans, thus more girls, thus more heartless ball-maulers ready to dock your fleeting ranking. It does this while also producing males who can maul balls yet cannot dent the big three.

“Everyone that’s playing these Grand Slams, I think everyone can beat everyone,” said Riske, who toppled French Open champion Ashleigh Barty on the way to a stern Wimbledon quarterfinal loss to Serena Williams. “And that’s something I think when I first started out, maybe that wasn’t necessarily the case.

“I feel like the young generation that has, you know, made a presence on the tour, I feel like they’re getting younger and younger and really making statements. I think it’s really cool, and I think it does say a lot about the depth of the sport.”

Muguruza, the world’s No. 1 player only two years ago, just finished a Grand Slam year of exits in the fourth round, fourth round, first round and first round here to Riske.

“Before, I remember even not that long ago, a few years ago, it was different,” Muguruza said. “You know, you had a difference between the top players and not top players. Now you feel like if you’re not 100 percent every day, you know, matches like today, you know, opponents are playing just great. Yeah, it’s much more equal, definitely.”

Asked whether she might rediscover the recipe, “If I would know the recipe, believe me, I would do it all the time. I did perform at a very high level of tennis. It’s very difficult to perform that. And like we were talking before, I feel like now everybody is playing great. You know, I feel like I come to the U.S. Open, and you feel all the girls can win, and they’re playing incredible. Everybody is a threat. Yeah, I mean, that’s really the difference now.”

Now it takes a bustling brain to comprehend all the biographies, the possibilities, the prodigies. Players go up. Players go down.

Naomi Osaka, who had never reached a Grand Slam quarterfinal until last U.S. Open but who clearly had exhilarating talent, won that U.S. Open and then the 2019 Australian Open. She reached No. 1 in the world. She remains 21.

By March, along came the fresh threat of Andreescu, still 19 and ranked 15th. She showed a knack for toppling top players, won the near-Slams at Indian Wells and Toronto and emerged as a hip pick to win here. On Tuesday she won briskly against American qualifier Katie Volynets and said of her confidence across the past 12 months, “I think it skyrocketed.” That always mattered, but maybe now it matters more than ever, in a world of vast talent and small margins.

By July, along came Coco Gauff, still 15, not yet even 15½ . While it’s too soon to make forecasts for her, she does demonstrate how the future won’t stop coming.

Amid all the factors, Osaka, having reached No. 1, had something of a swoon, departing Roland Garros in the third round and Wimbledon in the first.

Such swoons have grown ever more understandable as a sport threatens to set fresh standards in the human pursuit of parity.

“Plot twist,” Osaka said of her post-Australia season. “But the kind of plot twist that makes you want to keep reading it.”