Ferrari's Leclerc fastest at Italian GP first practice ahead of Russell
The Monegasque, whose home race follows next week, lapped the Enzo e Dino Ferrari circuit in a best time of one minute and 16.990 seconds.
George Russell lapped second fastest for Mercedes, 0.104 seconds behind and also on soft tyres, with Ferrari's Carlos Sainz third.
Red Bull's championship leader Max Verstappen, winner of four of six races so far, was fifth fastest and 0.250 off the pace with Mexican teammate Sergio Perez fourth.
Verstappen complained over the radio of a lack of grip and went off track several times, bouncing across the grass and gravel at Acque Minerali.
Seven-times world champion Lewis Hamilton, racing in Italy for the first time since his move to Ferrari next season was announced, spun his Mercedes onto the grass at the same complex of corners with 22 minutes to go but was able to continue.
The Briton was seventh on the timesheets, behind RB's Yuki Tsunoda.
McLaren's Lando Norris, winner in Miami last time out for his first career win, was eighth with teammate Oscar Piastri ninth and Aston Martin's Fernando Alonso completing the top 10.
Williams' Alex Albon brought out red flags briefly when he pulled over early in the session. The team said the engine shut down after he went over a kerb and the cause was being investigated.
British teenager Oliver Bearman was back in a Formula 1 car after standing in for an unwell Sainz in Saudi Arabia, this time replacing Kevin Magnussen at Haas for the first practice session as part of six such outings this year.
Bearman was 15th fastest, with teammate Nico Hulkenberg last on the timesheets.
