Quickest in both sessions on Friday, he beat Red Bull’s Max Verstappen by just .017 with Formula One champion Lewis Hamilton .083 back from Bottas in third in warm and sunny conditions.
Hamilton leads the championship from Bottas by 47 points after winning five of the first eight races in his bid to equal Michael Schumacher's record seven F1 titles. Later Saturday, Hamilton will aim for a record-extending 95th pole position. But Bottas test drove here with Williams back in 2012 and so far has looked more assured than Hamilton, who hasn't driven here before.
Hamilton looked set to beat Bottas when he led on the first time split, only to fall back in the second and third sectors. Verstappen then went out for one last run late in the session and split the two Mercedes in an encouraging sign for Red Bull on a circuit which has ultra-fast corners.
Mugello’s 5.2-kilometer (3.2-mile) Autodromo Internazional track, nestled amid a stunning backdrop of the Tuscan hills, usually hosts MotoGP and is hosting an F1 race for the first time. Drivers were full of praise for it after Friday's opening day.
Lance Stroll was fourth for Racing Point, which uses Mercedes engines, while Pierre Gasly was fifth but pushed a bit too hard late on and skidded off track. The Frenchman won last Sunday’s Italian GP for his first F1 win.
Ferrari is competing in its 1,000th F1 race and was once the team to beat in the way Mercedes is now. Schumacher won five straight titles with the famed Italian manufacturer from 2000-4, but this season has been one of Ferrari's worst in memory.
While Charles Leclerc was seventh fastest in final practice, Sebastian Vettel was a demoralizing 18th on a circuit which is actually owned by Ferrari and which he tested on as recently as June.
Williams driver George Russell had to come back into the pits with about 20 minutes later because a brake failure.