San Francisco Frontiers - Leclerc completes practice clean sweep in Spain

The 24-year-old Monegasque, who leads the Dutchman by 19 points in the title race, clocked a fastest lap of one minute and 19.772 in his Ferrari to outpace the Red Bull man by 0.072 seconds.

After their resurgence on Friday, Mercedes confirmed their improved form with George Russell heading seven-time champion Lewis Hamilton in third and fourth ahead of local hero Carlos Sainz running a new chassis in the second Ferrari.

Sergio Perez was sixth in the second Red Bull, within half a second of Leclerc to raise the prospect of a fiercely competitive qualifying session later on Saturday.

Like Sainz, Lando Norris took a new chassis on his way to seventh for McLaren ahead of Kevin Magnussen of Haas, Valtteri Bottas of Alfa Romeo and Esteban Ocon of Alpine.

The session was uninterrupted, but Mick Schumacher had to abandon his blazing Haas car after a major brakes blaze in the pit lane.

On another hot day in Catalonia, the air temperature was 30 degrees and the track 43 degrees, conditions certain to make tyre wear a key strategic factor in both qualifying and Sunday’s race.

To the relief of many observers, Mercedes appeared to have maintained their Friday improvement while Aston Martin, at the centre of ‘copy-cat’ allegations the previous day, seemed to gain little advantage from their controversial ‘green Red Bull’ upgrades package.

Red Bull’s special advisor continued to suggest that intellectual property (IT) may have gone to the Silverstone based team, linking it to the fact that seven former Red Bull staff had moved from Milton Keynes.

"As things stand, copying isn’t forbidden," Marko had told Sky Sports Germany.

"But you must also take into account that seven people were poached from us and that our chief aerodynamicist (Dan Fallows] joined Aston Martin with a disproportionately high fee.

"There are still some facts that we are checking. We will look into it in detail. There is evidence that data was downloaded."

Fallows left Red Bull to join Aston Martin as technical director.

As that speculation continued, much of the on-track action centred on drivers out in new chassis, or running new engines.

These included Norris of McLaren who was first to lap in his new chassis to be followed by Bottas of Alfa Romeo, powered by a new engine, and Sainz, in a new red Ferrari chassis.

Sainz swiftly went top to be overhauled by team-mate Leclerc while fires affected Pierre Gasly’s Alpha Tauri and Schumacher’s Haas, the German’s car suffering a major brakes blaze that spread across a rear quarter.

Verstappen was slow to join the fray and complained that this car "doesn’t turn in at low speed", but he rose to second by mid-session, before being overhauled by a revived Russell.

The champion responded, but he could not beat Leclerc's 1:19.772 as Hamilton moved briefly to third, proving he and Mercedes will be a serious threat later in qualifying.

J.Peterson--SFF