The 19-year-old became the first American teenager to triumph at Flushing Meadows since Serena Williams in 1999.
Sabalenka will be the new world No 1 on Monday after a consistent year in which she won the Australian Open and reached the semi-finals at the French Open and at Wimbledon.
But that will be scant consolation for the 25-year-old from Belarus after she put herself in a position to win her second Grand Slam title only to fold as Gauff claimed her first, thrilling a raucous crowd with a memorable victory at Arthur Ashe Stadium.
Gauff, who reached her first slam final at Roland Garros last summer, losing heavily to Iga Swiatek, said: “It means so much to me, I feel like I’m a little bit in shock. My French Open [final] loss was a heart-breaker for me, but God puts you through trials and tribulations and that makes this even sweeter.”
“I just knew if I didn’t give it my all I had no shot at winning. Aryna is an incredible player and deserves to be number one.”
Taking the microphone and before receiving the trophy from Billie Jean King on the 50th anniversary of equal prize money, Gauff said: “Thank you first to my parents.
Today was the first time I ever saw my dad cry. He thinks he’s so hard but…he took took me to this tournament when I was young to watch Serena and Venus (Williams) compete, so it’s incredible to be on this stage.
“Thank you so much to my team. I know it’s been a long month but your faith has never wavered.
“And thank you to the people who didn’t believe in me. I tried my best to carry this with grace. To those who thought you were putting water on my fire, you were really adding gas to it and now I’m burning so bright.”
How Gauff won the US Open…
Carrying home expectation, Gauff began nervously, dropping serve in the opening game before Sabalenka threw in errors of her own to help the American pull back to 2-2.
But the match was being played entirely on the racket of the soon-to-be world No 1 and she landed more than she missed in winning four games in a row.
The second seed took a medical time-out for treatment to her left thigh after finally getting on the board in the fifth game, and the delay gave Gauff some unwelcome time to think.
A loose service game gave Sabalenka a way back in but Gauff responded brilliantly with another break and closed out a victory in stunning fashion.
There were tears of a different nature for Sabalenka, who said as the crowd applauded: “You guys could have cheered like this during the match!
“I just want to say congrats Coco, you played unbelievable. And to your team. You guys deserve this title. Many more to come I’m pretty sure. I hope we’re going to play many more finals – different result hopefully.”
Sobbing heavily, the Belarusian added: “I want to send a lot of love to my family, sorry about this result.”
