Alexandra Trusova just beat her training partner Anna Shcherbakova to retain her world junior title in Zagreb.
Trailing by just half a point from the short program, Trusova fell on a quad Lutz at the start of her free skate.
But the 14-year-old landed two quad toeloops to post a score which Russian national champion Shcherbakova could not match.
Ting Cui took bronze for the United States.
Trusova exacts revenge
The scene was set for a thrilling duel between the two training partners of Olympic champion Alina Zagitova with just 0.37 points separating them after the short program.
They were the last two athletes to go with reigning world junior champion Trusova skating first.
And with three quads in her routine against Shcherbakova's one, it was Trusova's contest to lose.
Things did not start well as she fell on her first jump, a quad Lutz.
But she quickly hit back with a quad toeloop-triple toeloop combination and then another clean quad toeloop.
Despite a couple of her later jumps looking slightly ragged, it was a powerful performance from Trusova who scored 150.40 for a total of 222.89.
Shcherbakova needed to be near-perfect to eclipse that mark but she also erred on her opening quad Lutz, taking a step on landing.
And while her skate was the more elegant of the two, it lacked the technical firepower of Trusova's display.
Having edged out her Sambo-70 club colleague by less than a point in December's national championships in Saransk, Shcherbakova was unable to come through this time.
A score of 147.08 gave her a total of 219.94 with Trusova winning by almost three points.
Trusova joins an elite group with Adam Rippon (2008-09) and Elena Radionova (2012-13) the only other skaters to win two world junior singles titles.
Zagitova won this event in 2017, with Olympic silver medallist and double world champion Evgenia Medvedeva taking gold in 2015.
Cui ends American drought
Ting Cui produced a fine free skate to become the first American female world junior medallist since Gracie Gold in 2012.
The 16-year-old from Baltimore fell on her last jump, a triple flip, but was otherwise near-flawless as she scored 126.72 points for a total of 194.41.
That guaranteed her a medal with just the two Russian stars to come.
Fourth place went to another Russian, Kseniia Sinitsyna, with Japan's Yuna Shiraiwa in fifth spot.