Gauff beat Aryna Sabalenka 2-6, 6-3, 6-2 at the U.S. Open to win her first major tournament.
She had been close to winning her first big tournament before, but this time she finally did it.
After she won, former U.S. President Barack Obama sent her a message on X, which used to be called Twitter, to tell her how happy he was for her.
"Congratulations to @CocoGauff, the winner of the US Open! Obama wrote on Twitter, "We couldn't be more proud of you on and off the court, and we know the best is yet to come."
Gauff is only 19 years old, so it's likely that she has a lot more big wins in her.
She is also expected to become the best women's player in the world soon.
She will be one of the favorites to win the WTA Finals at the end of the year and the Australian Open in January.
The men's final, which will take place on Sunday between Novak Djokovic and Daniil Medvedev, is the only match left at the U.S. Open.