For much of the first set in her fourth-round match at Wimbledon, against Simona Halep, Cori (Coco) Gauff held her own. That, in itself, was impressive: Gauff is fifteen years old and came into Wimbledon ranked three hundred and thirteenth, whereas Halep was the seventh seed, a Grand Slam champion and a former world No. 1. And yet Gauff was striking her backhand dangerously, serving hard, closing in on the net, and withstanding long rallies. If anything, Halep was the one showing nerves, at one point serving three consecutive double faults. But Halep dug out the first set, and, as the second progressed, the points started to slip away from Gauff quickly. Her forehand, a weakness all day, became more erratic, and Halep began to pick on it. Halep had a good read on Gauff’s preternaturally powerful serve all day, and she pressured it more and more. Gauff, whose stomach was bothering her, called the trainer to the court. Gauff’s shoulders slumped; she appeared dejected. Match point came quickly. Serving down a set and two games to five in the second, with the score 15–40, Gauff sent the ball to Halep’s backhand, close to her body, and then calmly redirected Halep’s crosscourt reply down the line into the ad corner—a winner against most players, but Halep, one of the quickest on tour, was able to block the ball and send up a lob. Gauff took it out of the air at midcourt, sending it into the opposite corner; Halep, already on the move, scrambled to the ball and struck a forehand that dove toward Gauff’s feet. Gauff leaned down and, with a delicate touch, drop-volleyed the ball over the net. Far from Halep’s reach, the bounce died in the grass.

Of course it did. This was not the first match point that Gauff had saved during the tournament. (In her third-round match against Polona Hercog, Gauff had faced two match points.) Nor would it be the last. A point later, Halep sent a return barely wide.

For a brief moment, it did not seem possible that Gauff could lose the match—or any match, ever. Over the course of a week, millions of people, not only in the United States but all over the world, had tuned in to watch Gauff, and very, very few of them had ever seen her be defeated. Gauff had never lost a match in the main draw of Wimbledon. Winning was all she had ever done.

Of course, it made sense to expect that, facing a fifteen-year-old, Halep would benefit from her years of experience—and, in the end, they surely helped. But experience can be double-edged, as Halep understands. In June, Halep was knocked out of the quarterfinals of the French Open by a seventeen-year-old, Amanda Anisimova. Two years before, she lost in the French Open final, to Jelena Ostapenko, an unseeded twenty-year-old who swung freely, almost innocently, as if she wasn’t aware of how rare these chances are and how painful it would be to lose. Halep knew.

And now, in a way, Gauff knows, too. As she left the court, the crowd stood to cheer for her. No one could feel anything but admiration for the way she had played, not only against Halep but throughout her improbable run. But she could not hide her own disappointment. Her smile was gone.

All but one leave Wimbledon a loser. It’s absurd for an untried fifteen-year-old to think that she could become the champion. That confidence is a big reason she may win, and soon—as big a reason as her powerful serve, her sound shot selection, her athleticism, and her deft touch. In the meantime, how she handles losing will likely be as big a test as any opponent. It will be a test for her many new fans, too.