Gauff, from Delray Beach, Fla., is the youngest player to reach Wimbledon’s round of 16 since Jennifer Capriati advanced all the way to the semifinals in 1991, also at 15. She is the only player in the women’s field who is so young that tournament officials have to limit her playing time under rules designed to protect players under 18 from burnout.

On Monday, Gauff will meet No. 7 seed Simona Halep, the 2018 French Open champion and a four-time Grand Slam finalist.

Gauff, who earned her spot in the main draw as a qualifier and is ranked 313th in the world, was asked afterward how she maintained her composure when she was trailing. “I always knew I could come back no matter what the score was,” she said, “and I just kind of went for my shots.”

Coco Gauff rallied from being down two match points to beat Polona Hercog. Afterward, she said the crowd helped motivate her: “Even when I was down match point, they were still cheering me on.” (Ben Curtis/AP)