Formula 1 leader Oscar Piastri led Lando Norris in a McLaren one-two in first practice for the Emilia-Romagna Grand Prix that ended early on Friday after Gabriel Bortoleto crashed his Sauber.
Australian Piastri, winner of four of the last five races, lapped the Imola circuit with a fastest time of 1:16.545 on the softest tyre compound with Norris 0.032 seconds slower on a sunny afternoon.
Piastri leads Norris by 16 points after six races, with the 24-round season now starting its European phase after an opening run in Asia, the Middle East and United States.
The session was red-flagged and did not restart after Brazilian rookie Bortoleto crashed into the tyre wall with some three minutes remaining. He stepped out unhurt.
Carlos Sainz was third on the timesheets for Williams, 0.052 off the pace, with Mercedes' George Russell a further 0.002 slower.
Seven-time world champion Lewis Hamilton, limbering up for his first race in Italy as a Ferrari driver, was fifth and 0.096 off the pace.
Pierre Gasly was sixth for Alpine with Red Bull's four-time world champion Max Verstappen seventh, William's Alex Albon eighth and Bortoleto ninth with teammate Nico Hulkenberg completing the top 10.
"I can't rely on the rear. It feels like I'm drifting everywhere," complained Verstappen, last year's winner at Imola, over the radio.
Mercedes' 18-year-old rookie Kimi Antonelli, the only Italian on the starting grid and preparing for his home debut, was 13th fastest.
Argentine rookie Franco Colapinto, making his debut for Alpine after replacing dropped Australian Jack Doohan, lapped 17th fastest.
Ferrari's Charles Leclerc, who was unwell on Thursday and skipped his media duties, was 12th and ran wide into the gravel at one point. He also complained that his helmet was lifting.