Behind Davydova and Ermakova, whose top spot was all but a surprise, came Japanese Olympic and world silver medallists Miya Tachibana and Miho Takeda with 98.000.
Third was the American pair of Bartosik and Koslova, ahead of Spain's Gemma and Mengual and France's Dedieu and Thibaud.
Russian duet lead way to final
The duet free routine qualifying takes place on Tuesday evening, while the duet final will be on Wednesday.
USA's Artistic Swimming performance at London 2012
Russia’s near-perfect synchronised swimming routine at London 2012