Charles Leclerc led teammate Carlos Sainz in a Ferrari 1-2 during Friday's first practice session at Imola.
In a wet hour of running, Leclerc clocked a time of 1:29.402 on the Intermediate tyre to finish the best part of a second clear of Sainz.
Max Verstappen and Red Bull were next up in third, with Haas using the tricky conditions to complete the top five positions.
The full results from FP1 for the Emilia Romagna GP can be seen below: