Red Bull's Max Verstappen was second in the Italian sunshine, with Ferrari's Charles Leclerc a surprising third and Bottas's world championship-leading teammate Lewis Hamilton only fourth.
Hamilton has a 47-point lead over Bottas after eight races, with the Finn needing to turn things around to prevent the Briton from accelerating to a record-equalling seventh title.
It was the fifth time in a row that Bottas, who has so far won only the opening race in Austria in July, had been fastest in first practice.
The race is also a celebration of Ferrari's 1,000th championship race with their cars carrying a retro burgundy livery harking back to their Formula One championship debut in 1950.
Bottas lapped with a best time of one minute 17.879 seconds, with Verstappen 0.048 slower around the scenic track in the hills north of Florence.
Leclerc was 0.307 off the pace, giving some hope to Ferrari after dismal races in Belgium and last weekend's Italian Grand Prix at Monza.
Pierre Gasly, the surprise winner of that last race for Red Bull-owned AlphaTauri, was fifth fastest.
Most of the drivers were experiencing the fast, sweeping 5.2 km track -- more associated with MotoGP racing -- for the first time.
Friday was the first time paying spectators had been allowed to attend a race in a COVID-19-hit season, with some 2,800 a day allowed in. (Reporting by Alan Baldwin in London, editing by Jason Neely)