At 20, Ostapenko is the youngest French Open champion since Iva Majoli, who won at 19 in 1997. There was a clear opportunity for a breakthrough at this French Open, with Ostapenko’s childhood idol, Williams, now 35, taking a hiatus for the birth of her first child, and with No. 1 Angelique Kerber in an extended slump.

But few would have imagined that Ostapenko, who had not gone past the third round in her first seven Grand Slam singles tournaments, would be the one to capitalize. Before arriving in Paris, she had prize earnings of $1,288,260 for her entire career. Saturday’s victory was worth $2,351,097.

“We didn’t have the big names here,” said Chris Evert, the seven-time French Open champion. “But I tell you what: A star was born today, and I’ve got to say, it’s so great for women’s tennis. We need fresh young blood.”

It may also be good for female coaches, who remain a rarity on the WTA Tour. Ostapenko was long coached by her mother, Jelena, and she added Anabel Medina Garrigues, a fine clay-court player from Spain, to her coaching team in April.

“Of course, it was always nice to work with my mom,” Ostapenko said in a postmatch interview, “but the thing that she’s my mom and coach sometimes is also tough because we see each other almost 24 hours a day, and sometimes we get tired of each other.

“We added something different just to see if it works, and I think it worked pretty well.”

Ostapenko’s relentless, tight-to-the-baseline playing style has elicited comparisons to a young Seles. But unlike Ostapenko, Seles hit with two hands on both her forehand and her backhand. Seles was also a much more unflappable competitor and a consistent ball striker.

Ostapenko has tended to be unpredictable and volatile. Last year she threw a racket during a tournament in Auckland, New Zealand, and it bounced off the court and struck a ball boy. She said she had worked on her composure. But on Saturday there were still plenty of shrieks and wounded glances in the direction of her support team. She even gestured at her mother to leave the stadium at one stage.