Tears flowed as ninth seed Korneeva fought back from a set down against compatriot and close friend Mirra Andreeva at Rod Laver Arena on Saturday, triumphing 6-7 (2-7) 6-4 7-5.
The exhausted players, both just 15 years old, embraced at the net after an epic encounter that lasted three hours, 17 minutes.
But it was almost over at the start of the second set when Korneeva - battling leg and stomach complaints - considered withdrawing.
Korneeva dug deep to resume the fight and reaped the ultimate reward in her first attempt at a grand slam.
"I couldn't play my game and show my best ... I couldn't run a lot, but mentally it was good," Korneeva said.
"I'm so proud of myself because I can't believe that I could win with these problems (injuries).
"It's my first grand slam and I hope not last one ... I'm so proud of myself and my mental game."
Korneeva wasted two championship points in the 10th game of the third set - the second with a double-fault - as Andreeva broke to stay in the match at 5-5.
But Korneeva broke straight back and won her final service game to love, clinching the championship in her first attempt at a junior grand slam.
"It's not our last battle," Korneeva told her emotional opponent post-match.
"We will have a lot of good matches when you will win, when I will win ... it was a hard battle."
Korneeva, who idolises tennis legends Serena Williams and Rafael Nadal, is the first Australian Open girls' champion from Russia since Elizaveta Kulichkova in 2014.
She follows in the footsteps of fellow Russians Ksenia Pervak (2009) and two-times winner Anastasia Pavlyuchenkova (2006-07).
Korneeva also joins a girls' title honour roll 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.
The ensuing boys' final was also a thriller as No.3 seed Alexander Blockx became the first Belgian to win the title with a 6-1 2-6 7-6 (11-9) triumph over American Learner Tien.
"It was one of my hardest battles of my life," Blockx said.
Blockx will hope to join an illustrious group of former boys' title winners - including Nick Kyrgios, Alexander Zverev, Stefan Edberg and Andy Roddick - in going on to have a successful career on the men's tour.
The 17-year-old was also runner-up with Brazil's Joao Fonseca in the boys' doubles this week.
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