The 16-year-old won silver at the 2012 Winter Youth Olympics in Innsbruck but is on course to go one better in Croatia, while Jenna McCorkell survived the cut.
Sotnikova skated clean to score 67.61, smashing her personal best by six points to sit at the summit.
Reigning European and world champion Carolina Kostner of Italy could only manage 64.19 for second place after falling on an early combination, while Italian veteran Valentina Marchei staked her claim for a first major medal by taking third with 58.22.
Meanwhile, Great Britain's sole representative McCorkell scored 47,17 points to sit 19th, with the top 24 going through to the free skate.
