In the women’s final of the French Open on Saturday, Jelena Ostapenko was fearless. The word was inescapable. It was repeated on television, on Twitter, in the headlines that announced her 4–6, 6–4, 6–3 win over Simona Halep. It was felt in the singe of every forehand she fired, heard in every shrieking grunt, seen in every backhand return she ripped—whether for a winner or an error. It was evident in the way that she broke Halep’s serve at love to start the match, in the way she kept gunning her shots when she was down a set, 0–3 in the second, and facing three break points. She went for a winner with every shot.

That has always been her style. The surprise was that, this time, it worked—not once, but in match after match in the tournament, and during the final, from beginning to end. In the first game, she roped a backhand half an inch over the highest part of the net, landing the ball just inside the corner down the line. On match point, she did it again. “She’s hitting as hard as she can down the line from nowhere,” the Swiss player Timea Bacsinszky said, after Ostapenko beat her in the semifinals. “I mean, who tries that? It’s like one out of ten.” Against Halep, Ostapenko gambled with those odds and hit the mark half the time. That was enough.

Ostapenko just turned twenty. Coming into the French Open, she was ranked forty-seventh in the world. She had never won a W.T.A. tournament. She had never made it past the third round of a Grand Slam. She was attempting to become the first unseeded player to win the French Open in the Open era, the first Latvian ever to win a major, the youngest player to win a Slam in more than a decade. She was facing the favorite. It was natural to assume that she would eventually tighten; that she would feel the pressure and crack; that she would show flashes of promise but ultimately lose to the more experienced player. At some point, she would begin to miss and would become scared. She would doubt herself. It was only human.

But that is not what she did. When she began to miss—when it appeared to everyone watching that she was lost—she told herself to “enjoy the match and to try to fight for every point,” she said afterward. Which is the kind of response that tennis players often give, the kind of cliché that makes athletes seem like the worst interpreters of their own experience. Who enjoys a beatdown, especially one that takes place with nearly $2.4 million on the line and people watching around the world, and with a giant screen set up to show the match in the middle of your home town? But there is no good reason not to take Ostapenko at her word. She didn’t adjust; she didn’t change a thing. She wasn’t discouraged by hitting fifty-four errors, more than four times as many as her opponent. She didn’t think. She just did.

She was—it was obvious—totally present on every shot, in a way that seems almost impossible. It was as though she were unaware of the occasion, unaware of her opponent’s preternatural ability to avoid mistakes, unaware of her own mounting errors. She was simply hitting the ball as hard as she could. She won because she was not afraid to lose.

A tennis court is marked out by white lines and walled off from the real world. Emotions of all kinds are heightened but also simplified. Those who thrive in that confined space tend to be the ones who can live entirely, unself-consciously, within it. Most of a tennis player’s career, in fact, is pointed toward that narrowing of her world. She drops out of a normal school. She practices the same patterns, day after day. She travels all over the world, but the Hyatts and Marriotts look largely the same. She has coaches—sometimes, as in Ostapenko’s case, initially her own parent—and physios and trainers, to keep her focus within the lines. She learns that thinking is the enemy of action. And, in that, she is often right.

Simona Halep, by contrast, is one of the most cerebral players on the tour. She is, to my mind, a geometer, the most artful constructor of points. She varies rhythm, pace, placement, pattern, and speed. She puts her opponents under pressure with the depth and weight of her shots, and sees winning angles where most would see the loss of a point. On clay, where the power of most players’ shots is blunted, she is especially effective. Her quickness and footwork are unmatched. There are great movers in the women’s game; she is the best.

But her mind can be a trap. Throughout her career, she has had, not infrequently, attacks of self-doubt. Her feet become tangled; her serve disappears. The court ceases to be familiar. She begins to lose, and becomes lost.

For the past year and a half, she has worked on this relentlessly. She has gone to Las Vegas and run in the desert, training her body to take over. She has improved her tactics, learning to open the court. She has improved her forehand, her serve. She has also worked with her coach, Darren Cahill, on trying to solve her own problems, instead of leaning on his support. Like Ostapenko, she has told herself to enjoy the game and to fight for every point. But unlike Ostapenko she has, very sensibly, been susceptible to the hollowness of those thoughts. She has, at times, given up.

In the quarter-finals of the Miami Open, in March, against Johanna Konta, after dominating the first set and most of the second, Halep let her lead slip away, and the match went to a third set. She called Cahill onto the court. (On-court coaching is allowed in W.T.A. matches, though not at the Slams.) “I’m so bad,” she said. “I’m ridiculous bad.”

“How are you going to fix it, then?” he asked. She shrugged him off and started listing her errors and double faults. “What do you want?” he asked. She refused to look at him. “You have an opportunity to make a difference,” Cahill said. “That's all I can say. You've been in this position many times before, and, most times, you’re coming out second best. Right now you have an opportunity to change things. It’s up to you. You can decide what you want to do here. You can go down this path, and that’s fine. Or you can take a deep breath, put your towel on your head, and try and get a little better in these situations. It’s as simple as that. It’s up to you. It comes from within.”

She kept venting. “Be brave,” he told her. She wasn’t listening. She continued to lash herself, went back onto the court, and lost.

After that match, Cahill ended their partnership. It was, Halep later said, “a shock.” And the story of the clay season was that the shock worked. They reunited five weeks later, and she went on a remarkable run, winning Madrid and making the finals at Rome, where she was comfortably ahead before turning her ankle. She played brilliantly through the first four rounds of the French, and then, when tested, she did what she said she would, and she fought. In danger of being blown out by Elina Svitolina in the quarter-finals, then down a match point, she played her best tennis.