Valtteri Bottas headed Mercedes team-mate Lewis Hamilton in Friday practice at the Tuscan Grand Prix as Lando Norris crashed his McLaren.
Norris put a wheel in the gravel on the exit of Turn Three, Poggio Secco, and spun into the wall. He was unhurt but the incident ended his session.
Bottas was 0.207 seconds ahead of Hamilton in second practice and was ahead in both Friday sessions.
Red Bull's Max Verstappen was third fastest, 0.039secs behind Bottas.
Norris' incident led to one red-flag period, and there was a second for a collision between Racing Point's Sergio Perez and Alfa Romeo's Kimi Raikkonen.
Perez was coming out of the pits and did not see Raikkonen on a flying lap on his outside, and as the Finn turned into the first corner his right rear wheel clipped the front right of Perez's car.
Perez has been given a one-place grid penalty by stewards.
Hamilton said he was not driving well and had a lot of improvements to make for the weekend.
"I was just trying to focus on improving my driving," he said. "There are not a huge amount of changes I need to make to the car.
"There are times as a racing driver there is no point changing the car because you are not driving well enough. There are areas I need to make a change but I will do that overnight and hopefully improve it tomorrow.
"I am trying to push it to the limit but there are sections - the last sector I have got that sorted. The first and second sector are a little bit weak for me, particularly the first sector, and there is plenty to come there."
Line ID @ufa98v2