Is this the end of Serena Williams’ historic and sport-changing run at the Olympics?

Every four years at the Summer Olympics, we hear a lot about dreams. Dreams followed, dreams chased, dreams that died, dreams that came true, dreams that were shattered in a matter of seconds. Most of the athletes who compete at the Games spend the vast majority of their lives dreaming.

Then there was Elina Svitolina. According to her, it had never entered her head, while she was awake or while she was sleeping, that she could do what she did against the Serena Williams in Rio on Tuesday.

“One of my dreams is to play her,” the 21-year-old Ukrainian said. “To beat her, I don’t think I was even dreaming of that.”

What happens when non-dreams come true? Svitolina found out when she stunned the world and herself by beating the top seed and defending gold medalist in women's singles, 6-4, 6-3. If it seems like a stretch that Svitolina never entertained the possibility of a victory, you probably didn’t see their last match, at the French Open in June. Serena’s 6-1, 6-1 thrashing would have left even the most confident of opponents feeling hopeless.

But this was a very different Serena than the ruthlessly efficient one that Svitolina faced in Paris. This was a Serena who came out of the gates slowly, who had struggled mightily against 48th-ranked Alizé Cornet in her previous match, who had already endured a first-round doubles defeat with her sister and who, perhaps most importantly, had pulled out of her previous event with inflammation in her shoulder. By the second set, Serena was grabbing that shoulder as her service speed began to drop. By the middle of the set, she was having trouble getting her serve in at all. After breaking for 3-3, Serena double faulted five times to hand the break back. Her downward spiral only accelerated from there.

Serena’s statements to the press afterward were terse.

“It didn’t work out the way I wanted it to,” said Serena, who committed 37 unforced errors in 19 games. “The better player won.”

While Serena was hindered, Svitolina did play well. Known for her solid backhand and sometimes-not-so-solid forehand, she took the rallies to the American when she could. While she managed just nine winners, she forced Serena into 17 mistakes. Svitolina, who is coached by Serena’s old rival Justine Henin, has always seemed capable of upsets in theory, if not in practice. Maybe this will convince her to dream a little bigger—or just start dreaming—in the future.

Is this the end of the Williams sisters’ long-running Olympic dream, which began 16 years ago in Sydney? Venus does have one more chance at a medal in Rio; she’s playing mixed doubles with Rajeev Ram. But by the time the next Summer Games come around in 2020, she’ll be 40 and Serena will be approaching 39. Nothing is impossible with those two, of course, but a trip to Tokyo will be a long shot.

At Wimbledon last month, Serena said she hadn’t prioritized the Olympics this time around, the way she did in 2012. She wanted a 22nd major title more than anything else, and she got it. If this is the last we see of Serena at the Games, it will mark the end of an historic and sport-changing run. With her sister, she helped make it cool for tennis players to care about the Olympics, and her record at them will be a significant part of her legacy. Only gold medals would do for the Williamses—Venus and Serena each have four; silvers and bronzes aren't their style. By now Serena's Olympic legacy extends beyond tennis. Other athletes in Rio sought her out for selfies and autographs, and Gabby Douglas, the 2012 all-around gold medalist in women’s gymnastics, called her a role model.

The Williams sisters first caught the Olympic bug from their father, Richard, who loved the Games and always wanted his daughters to play in them. In looking back at the notorious 2001 incident involving Serena at Indian Wells, Richard said he was especially appalled by the fact that the crowd was booing someone who had won a gold medal for the U.S. the previous year. I’ve wondered whether Richard’s love for the Olympics came from a similar place as Arthur Ashe’s love for Davis Cup. Both grew up in the segregated South (Williams was born in Louisiana in 1942, Ashe in Virginia in 1943), and Ashe once wrote that “winning a place on our national team would mark my ultimate triumph over all those people who had opposed my career in the South in the name of segregation.” Richard might have felt a comparable sense of satisfaction and vindication in seeing his daughters on the Olympic podium, listening to “The Star-Spangled Banner.”

Even without their father’s influence, though, it makes sense that the Williams sisters gravitated toward the Olympics. Their story has always been about impossible dreams, and the power to make them possible. No tennis players have brought as much gold home for their countries as they have.