Nico Rosberg edged Mercedes teammate and Formula One championship leader Lewis Hamilton in Friday's morning practice for the inaugural Russian Grand Prix.
The Mercedes pair has dominated all season and was again firmly in control despite an unfamiliar track making its debut on the F1 calendar.
Rosberg's fastest lap on the Sochi Autodrom was one minute, 42.311 seconds; 0.065 seconds ahead of Hamilton, who leads Rosberg by 10 points in the title race.
Jenson Button and Kevin Magnussen of McLaren were third and fifth fastest respectively, split by Ferrari's Fernando Alonso.
The Marussia team ran only one car in respect to its driver Jules Bianchi, who remains in a critical condition after last Sunday's accident in Japan.