Russia's Anna Shcherbakova, just 16 and making her world figure skating championship bow, led after the short programme on Wednesday.
With 81 points, Shcherbakova was ahead of Japanese 18-year-old Rika Kihira (79.08) with the free programme to come on Friday.
Another Russian, 24-year-old 2014 world champion Elizaveta Tuktamysheva, is third (78.86).
"I was nervous, controlled every movement and I am happy that all elements were successful," said Shcherbakova who pulled off a double Axel, triple flip and triple Lutz-triple loop combination in her skate to "O doux printemps d'autrefois".
However, the 16-year-old admitted she missed not having fans supporting her with Covid-19 restrictions meaning a ban on spectators at the Stockholm venue.
"A lot of people write that they support me from their homes. It is also very important for me.
"But I miss full stands of people supporting you before the start and during the performance. Maybe for this reason I was very nervous, but I understand why the restrictions are needed."
As Shcherbakova shone, her highly-regarded compatriot Alexandra Trusova, also 16, and a pupil of former superstar Yevgeny Plushenko, struggled in 12th place.
She scored just 64.82 points having been penalised heavily for not employing jump combinations.
In the pairs competition, Russia's Aleksandra Boikova and Dmitrii Kozlovskii, the 2020 European champions, finished the day ahead of China's Sui Wenjing and Han Cong.
Boikova, 19, and 21-year-old Kozlovskii scored 80.16 points with their Chinese rivals on 77.62.
Russia's Anastasia Mishina and Aleksandr Galliamov are third on 75.79.
Two-time world champions Evgenia Tarasova and Vladimir Morozov are fourth on 71.46 with the free programme to come on Thursday.
As well as world medals up for the grabs, the 2021 championships is key in deciding team make-ups for the 2022 Winter Olympics in Beijing.