Tears flowed on both sides of the net as third seed Efremova held her nerve against gallant Russian Tupitsyna, winning 6-3 7-5 at Rod Laver Arena on Sunday.
Tupitsyna broke down during the second set when a hamstring injury forced a medical time-out and halted her momentum as she mounted a fightback.
The 17-year-old led the second set 3-0, but won just two of the next nine games after returning to the court with her left thigh strapped.
Efremova showcased her maturity in steadying to become just the second French winner of the AO girls' singles crown, after 1999 champion Virginie Razzano.
The 16-year-old joins a list of girls' title winners that includes Evonne Goolagong Cawley (1970) and fellow former world No.1 Victoria Azarenka (2005), who both went on to claim the women's crown on multiple occasions.
Efremova was immediately on a video call to her mother - former professional player Julia Efremova - in France as she celebrated her victory on the court.
"It's always kind of tradition when I'm winning a tournament, every time I call her, or even semis even," Efremova said.
"Even if she sleeps, doesn't matter. This time it doesn't matter. It's exceptional.
"Sometimes she doesn't sleep because she's very stressed. I wanted to wake her up with the good news."
In the boys' final, No.7 seed Ziga Sesko became the first Slovenian to win the title with a 4-6 6-3 6-4 victory over American Keaton Hance.
The 17-year-old fought back from a set down in a high-quality contest, played under a closed RLA roof due to rain at Melbourne Park.
"Winning a grand slam is, I think, what every kid is dreaming of," Sesko said.
"So to be able to actually achieve it, I mean, I don't even feel it now, but I'm sure tomorrow or later on I will feel very, very special."
Sesko will hope to join an illustrious group of former boys' title winners - including Nick Kyrgios, Lorenzo Musetti, Alexander Zverev, Stefan Edberg and Andy Roddick - in going on to have a successful career on the men's tour.
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