Charles Leclerc has ended the opening practice session from the Russian Grand Prix weekend on top of the times, setting a 1:34.462.
The Monegasque driver, who has taken pole position at the last three events, was marginally ahead of Max Verstappen, who was less than a tenth of a second behind.
Daniil Kvyat, who will start from the back of the pit lane, saw his session come to an early end as he was forced to park up in the final sector with a suspected engine issue.
Kvyat was running a new Honda Spec 4 engine for the session, with Honda confirming that it was investigating the issue ahead of second practice later in the afternoon.
Towards the end of the session, there was a rear wing problem for Bottas, as his DRS seemingly failed to open on one side of the wing.
Drivers had to cope with a new slalom bollard system at Turn 2, with drivers told to go around three different bollards before rejoining the circuit.
However, the system caused problems for drivers that bailed out of Turn 2 too late to make the first and second signs.
At the end of the session, Ricciardo spun at Turn 10 backing into the barriers and damaging his rear wing.
The second practice session will get underway at 15:00 local time.
Bahrain International Circuit - Winter testing