Mercedes driver Valtteri Bottas wrapped up practice for the first Tuscan Grand Prix at Mugello on Saturday with the fastest time for the third session in a row.
The Finn completed his sweep by lapping the fast Ferrari-owned Italian track with a best time of one minute 16.530 seconds on soft tyres.
Red Bull's Max Verstappen was just 0.017 slower and looking like a threat for qualifying even though Mercedes have so far taken every pole position this year.
Bottas's team mate and six times world champion Lewis Hamilton, who is 47 points clear in the standings after eight races, was third fastest, with Canadian Lance Stroll fourth for Racing Point.
AlphaTauri's Pierre Gasly, surprise winner at Monza last weekend on a podium without the usual three top teams, was fifth fastest.
Charles Leclerc, seventh fastest, was the leading Ferrari ahead of the team's landmark 1,000th championship grand prix, with team mate Sebastian Vettel 18th.
George Russell failed to set a lap time in his Williams after suffering an apparent brake failure early on.
F1 teams warned not to stockpile
Formula One teams have been warned by the governing FIA not to subvert a budget cap due to be introduced in 2021 by stockpiling parts this year for future use, McLaren boss Zak Brown said on Saturday.
The American told reporters that the International Automobile Federation had issued a note to the 10 teams on the subject.
"The FIA are on top of what you can and can't do," he said ahead of the Tuscan Grand Prix at Italy's Ferrari-owned Mugello circuit.
"Because next year's car has a lot of carry-over parts, there's been conversations around people stockpiling this year, with no budget cap, for next year to allow you to spend next year's money more on 2022.
"So they are already on top of that. They actually issued another statement to the teams overnight on this particular issue."
Brown said he was not aware of any teams that had stockpiled.
He said the message from the FIA was essentially "don't run too fast because you might find we're going to change something."
Teams will have to operate within a $145 million budget cap next year, reduced to $140 million for 2022 and $135 million for 2023-2025.
Due to the Covid-19 pandemic sweeping new regulations have been delayed from 2021 to 2022, meaning next year's cars are essentially the same as in 2020.
Champions Mercedes spent $442 million in winning both titles last year, according to their 2019 accounts.
Brown also revealed that any new team seeking to enter the championship would now have to pay a $200 million fee, split equally among the existing 10 teams under a new five-year commercial agreement all have signed.
"The $200m is intended to really make sure that if someone is coming into the sport that they have the wherewithal to do it," he said.
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