Ferrari's Kimi Raikkonen and Sebastian Vettel set the pace in first practice at the Bahrain Grand Prix as Mercedes hid their true form.
Raikkonen was 0.202 seconds faster than Vettel. Mercedes pair Nico Rosberg and Lewis Hamilton were only 15th and 16th. Williams's Valtteri Bottas was third, from Toro Rosso's Carlos Sainz Jr and Red Bull's Daniel Ricciardo.
The second Toro Rosso of Max Verstappen was sixth, ahead of McLaren's Fernando Alonso and Sauber's Felipe Nasr.
Mercedes's unusual approach to the session was taken because conditions in the desert were very different from those that will prevail in qualifying and race.