Ultimately, she lost the match -- ending her career-best appearance at a major. She couldn't hide her disappointment. But despite being just 17 years old, she didn't lose sight of the bigger picture, and she wasn't going to let it happen again.
"Enzo [Wallart], my hitting partner, told me this match will probably make me a champion in the future," Gauff told reporters after the loss. "I really do believe that."
One year later and back in Paris, she's two victories away from the 2022 French Open title.
On Tuesday, Gauff, now 18, reached the first semifinals of her Grand Slam career with an impressive 7-5, 6-2 win over fellow American and longtime friend Sloane Stephens. Gauff was nearly flawless in her takedown of the 2017 US Open champion -- as she has been for much of the tournament. In her five matches at Roland Garros, she has yet to drop a set and hasn't needed more than 90 minutes on court.
"I feel so happy," Gauff told the crowd at Philippe-Chatrier after the match. "Words can't explain. Last year in the quarterfinals was a tough loss for me and I think that match really made me stronger, to better prepare for moments like today, and moments I'll face in the next round."
Gauff is just the third American in 20 years to reach a final four at a major before her 19th birthday. It's the latest achievement for the budding superstar.
Gauff became a global sensation at Wimbledon in 2019 when she stormed through qualifying as a 15-year-old and went on to beat longtime hero Venus Williams in the first round on Centre Court. She ultimately made a run to the fourth round, and has since been seen as the sport's next thing -- and a potential heir to replace the giant-Williams-Sisters-void once they eventually retire.
Since her star turn, she hasn't quite had the success of other teens, like 2021 US Open champion Emma Raducanu, but she has slowly but surely been progressing on all surfaces and moving up the rankings.
She won two WTA singles titles, most recently at Parma last year, and four in doubles, including her first 1000-level title of any kind in Doha (with Jessica Pegula). She reached a career-high ranking of No. 15 in April.
In the past, Gauff has said that nerves have gotten the best of her. But this tournament has felt different. She has a more relaxed mindset this time around, she said.
There have been few outward signs of stress or anxiety in Paris. She has looked calm and poised, even during the few challenging moments she has faced, and has been all smiles and laughter after each match, further enamoring herself to the French crowd with each victory.
On Tuesday, she told the rapt Philippe-Chatrier audience about her new attitude, on and off the court.
"Obviously I believe in myself," Gauff said. "Even last year I was too focused on trying to fulfill other people's expectations and I think it's just, enjoy life. No matter how good or bad my career is, I think I'm a great person. That's a message for all the young players out there that your results, even in life in general, your results or your job or how much money you make, doesn't define you as a person. Just know that if you love yourself, who cares what anyone else thinks."
So now Gauff, playing just for herself, will have the biggest opportunity ahead of her -- yet again -- on Thursday in the semifinals against unseeded 28-year-old Martina Trevisan. Many had looked ahead to a potential showdown between Gauff and 19-year-old Leylah Fernandez as an exciting glimpse to the sport's future, but Trevisan defeated Fernandez in three sets in Tuesday's first match.
Gauff's and Trevisan's paths to the moment couldn't be more different. Trevisan stepped away from the sport for several years because of an eating disorder, and made her way back by playing mostly small ITF events before finally making her debut in a major main draw in 2020. But both will be looking to advance to their first major final.
Trevisan beat Gauff in their only career meeting, in the second round of the 2020 French Open. It was just Trevisan's second Grand Slam and, as a qualifier, she knocked off Gauff in three sets en route to the quarterfinals.
But Gauff doesn't need revenge as motivation on Thursday. She has plenty of that as it is.
The winner of Thursday's semifinal would likely set up a clash with world No. 1 and 2020 French Open champion Iga Swiatek. For much of the spring, Swiatek has been the overwhelming favorite for the Suzanne-Lenglen Cup, as she earned clay titles in Rome and Stuttgart and is currently riding a 32-match win streak. But she showed signs of vulnerability during her fourth-round match against Qinwen Zheng and will first need to get past Pegula on Wednesday. Daria Kasatkina or Veronika Kudermetova await in the semifinals.
Gauff has spoken throughout the tournament about taking it one match at a time, and on Tuesday that meant she had to focus on her third-round doubles match with Pegula against Sania Mirza and Lucie Hradecka, which she later won. Only then would she start thinking about Trevisan or Swiatek.
And it seems like she'll be just fine, no matter what happens the rest of the week.
"I really am just enjoying the tournament, enjoying life," Gauff said on Sunday. "I'm not thinking about, you know, the end result. I'm just enjoying the match ahead of me and whatever happens, happens -- it's out of my control. I'm going to give it my best either way."