They grow up fast these days, and none faster than Coco Gauff.

In early July, she was a shaky tennis teenager possibly heading into the sport’s wilderness, struggling to answer questions about how someone who had once appeared so precocious, so destined for greatness, could still be waiting for her big moment.

In September, she is a U.S. Open finalist, the star attraction of her home Grand Slam tournament and the new face of her sport in America.

Gauff, the 19-year-old prodigy from steamy South Florida, beat Karolina Muchova of the Czech Republic, 6-4, 7-5, to reach her first U.S. Open singles final on a warm and heavy Thursday night at Arthur Ashe Stadium. Muchova’s all-court game and the strangest of atmospherics tested her as never before, but in the end the night went her way in front a crowd that exploded for her over and over along the way.

“Some of those points were so loud I don’t know if my ears are going to be OK,” she said in her on-court interview.

Gauff was controlling the match when a climate protest early in the second set caused a nearly 50-minute delay as the New York Police Department and security officials struggled to remove protesters, one of whom had used an adhesive to glue his feet to the concrete in one of the upper levels of the stadium.

At the time of the interruption, Gauff held a lead of 6-4, 1-0 and was playing as well as she needed to take advantage of a seemingly tight Muchova, who played with a black compression sleeve covering her right arm from her biceps to her wrist, and, she said, tape beneath the sleeve.

During the delay, Gauff and Muchova headed off the court and tried to stay loose in the locker room and the warm-up area. Muchova got a massage and jogged lightly in the hallway outside the locker room. Gauff, seemingly loose, wandered over to a worker from the United States Tennis Association and leaned over to see pictures of the protesters circulating on social media. She said later that she woke up Thursday morning thinking that a climate protest might break out, as they had at the French Open in 2022 and Wimbledon this year.

Maybe that was a premonition. Maybe it was preparation by a player with a well-earned reputation for always doing her homework. She earned her diploma on time in the spring of last year despite spending all her high school years on the pro tour. She and her family celebrated in Paris. then she won six matches at the French Open before losing to the world No. 1, Iga Swiatek, in the final on a day when she said the moment overwhelmed her.

The delay on Thursday took the early juice out of a capacity crowd of nearly 24,000 fans who arrived ready to celebrate a new American tennis queen a year after watching Serena Williams play her last match, signaling the end of an era for American tennis.

Over the past four years, Gauff has evolved into the most likely candidate to fill the void, breaking out at Wimbledon when she was 15 and making her French Open run last year. Since then, though, her progress seemed to stall, especially on the big stages, and she had yet to move past the quarterfinals of the U.S. Open, the tournament where the spotlight shines brighter on her than anywhere else.

Two months ago, this run, and a championship that is now one match away, didn’t seem possible, but Thursday night Gauff showed every reason it suddenly is. She has long had so many of the tools needed to join the sport’s elite — a dangerous serve, a tough-as-nails backhand, and the speed and athleticism that combine for the best court coverage in the women’s game.

In the past five weeks, she has learned just how to use those tools, stabilizing the shaky forehand that was her nemesis. Against Muchova, she mixed power forehands with looping ones, and she hammered serves while also slicing some into the corners. She cut backhands and charged the net. She took control of points and rallied with Muchova until the Czech star fumbled them away. She got her first match point on a feathered drop shot.

Gauff wobbled midway through the first set, losing three straight games after taking a 5-1 lead as Muchova started to hit out and pushed Gauff onto her heels. She lost her serve once more as she tried to close out the match at 5-3 in the second.

It would take another three games; one more break of Muchova’s serve; five more match points; a nearly endless, lung-busting, 40-shot rally filled with a slew of shots hit within inches of the net; and moon balls that floated 10 feet above it. Then she fought off one last sharp serve from Muchova and hung on until one last backhand sailed long.

New York has been hers since her first match of the tournament, and now this night, and a spot in the finals, was hers, too.