Gauff and Pegula dissolved the lead for 3-4, but Garcia and Mladenovic were simply in the groove.
Supreme reactions and acute-angled volleys carved the ball to the open sections of the court. A decider was required to split this in-form four.
Garcia placed the Americans on the back foot, arrowing a backhand pass for a 1-0 break. The French pairing sensed their chance and soared towards their second major together in style, as chants erupted across the whole stadium.
“Today this atmosphere, these are memories that we will never forget. It's as special or even more special than before,” added Mladenovic, also a champion here alongside Timea Babos in 2019 and 2020.
“Living that together with Caro, speaking of the energy, we had the impression that it was France against the U.S. It was like a Fed Cup match. It was amazing to see this crowd present for a final today. A lot of shivers and emotions, it was even more than in 2016."
Pegula, set to rise to world No.9 in singles and No.12 in doubles, paid tribute to the other trio on court on Sunday.
“Congrats Kiki and Caro, amazing. Second time Caro, Kiki you’ve won many times, it’s incredible,” stated the 28-year-old American.