Championship leader Sebastian Vettel topped the times for Ferrari ahead of his team-mate Kimi Raikkonen in Friday's second free practice for this weekend's Russian Grand Prix.
The four-time champion German and the Finn, who was fastest in the morning, made a bold statement of intent in a session that proved they are ready to end Mercedes' three-year domination.
Vettel clocked a best lap in one minute and 34.120 seconds to lead the way by two-tenths of a second with Finn Valtteri Bottas third ahead of his struggling Mercedes team-mate Briton Lewis Hamilton.
Three-time champion Hamilton, who is second in the title race seven points adrift of Vettel, has won twice at the Sochi Autodrom where Mercedes have led every lap and won every race since the event began in 2014.
Dutch teenager Max Verstappen was fifth, despite stopping on circuit following a loss of power, ahead of his Red Bull team-mate Australian Daniel Ricciardo.
Brazilian Felipe Massa, showing some of his best form again this season after taking a u-turn on retirement, was seventh for Williams ahead of German Nico Hulkenberg of Renault, Dane Kevin Magnussen of Haas and Mexican Sergio Perez of Force India.
The session left champions Mercedes scratching their heads as Ferrari proved they are capable of easy supremacy on a track where no other team has ever enjoyed success.