PARIS - Coco Gauff sat plain-faced in her French Open changeover chair after moving one set away from her first Grand Slam final at 18 — just 18! — and calmly snacked on some cut-up pieces of pineapple and other fruit, seemingly without a care in the world.

Her opponent in Thursday’s semifinals at Roland Garros, Martina Trevisan, was taking a medical timeout so her right thigh could be treated and taped by a trainer. It was the sort of delay that might rattle some players, might make them slow down, relinquish momentum, think too much about what’s at stake.

Not Gauff. Not on this sunny, breezy afternoon at Court Philippe Chatrier. When the American arrived in Paris, she celebrated her recent high school graduation by posing for cap-and-gown photos near the Eiffel Tower while holding her diploma. After wrapping up a 6-3, 6-1 victory over the 59th-ranked Trevisan, Gauff will be back in that stadium on Saturday to face No. 1 Iga Swiatek for the championship.

“I’m in a mindset now like: ‘It doesn’t matter.’ I mean, I’m going to be happy, regardless. My parents are going to love me, regardless. So I’m just going to go into it like another match,” the 18th-seeded Gauff said. “I mean, yeah, it’s a Grand Slam final, but there are so many things going on in the world right now, and especially in the U.S. a lot of stuff is happening right now, so I think it’s not important to stress over a tennis match.”

“I’m a little bit in shock right now,” Gauff said with a chuckle after using her still-improving forehand to open up the court and her long-terrific backhand to seal points against Trevisan. “I didn’t know how to react at the end of the match. I have no words to describe how I feel.”

Swiatek, who won the 2020 French Open, is on a 34-match winning streak after eliminating No. 20 Daria Kasatkina 6-2, 6-1 on Thursday. Now, in Swiatek, comes someone who will present a much tougher test and will require a higher level of quality.

Swiatek has won her past five tournaments, last losing in February, against 2017 French Open champion Jelena Ostapenko. The only Polish player to win a major singles title in tennis is now on a winning streak that equals one Serena Williams had in 2013. The only longer run this century was a 35-match unbeaten stretch by Venus Williams in 2000.

With only faint wisps of clouds overhead and the temperature hovering around 75 degrees Fahrenheit (about 25 Celsius), the two women’s semifinals followed a similar pattern. Swiatek and Kasatkina were even at 2-all. But Swiatek claimed 10 of the last 11 games.

The men’s semifinals are Friday, with 13-time French Open champion Rafael Nadal playing No. 3 seed Alexander Zverev, and 2014 U.S. Open champion Marin Cilic facing No. 8 Casper Ruud.