Leclerc headed Lando Norris or Lewis Hamilton at the end of the opening hour, a session dominated by the presence of unfamiliar names.
A total of six rookies took part in the session, seven including Jack Doohan who is making his full-time F1 debut this weekend.
Ferrari made a first in F1 history with its selection, promoting Arthur Leclerc to drive alongside his brother, Charles.
It marked the first time brothers had ever driven for the same team in the same session.
Elsewhere, McLaren had academy member and Toyota sports car driver Ryo Hirakawa in for Oscar Piastri, while Felipe Drugovich replaced Lance Stroll at Aston Martin.
Ayumu Iwasa filled Yuki Tsunoda’s RB, Luke Browning for Alex Albon at Williams, and Isack Hadjar for Max Verstappen.
It was an inauspicious start for the Frenchman, who looped the world champion’s Red Bull Racing at the end of the back straight in the early minutes.
The presence of the rookies and the timing of the session meant there was limited value in the hour for most teams.
The weekend’s meaningful running happens as the sun sets, making Free Practice 1, held in the afternoon sun, misrepresentative.
Still, it afforded them the opportunity to assess the basics, such as ride height and wing levels.
RB has a new front wing this weekend, Iwasa carrying a large aero rake as the squad assessed the development.
It was the regular names who headlined the session, with George Russell and Lewis Hamilton topping it for the first quarter of an hour before Lando Norris logged a 1:25.710s.
There was little between the two squads, and with Sergio Perez only half a second away for Red Bull Racing it suggested it would be at least a three-way scrap at the top of the timesheets.
The unknown was Ferrari, given Arthur Leclerc’s inexperience and program, as Charles Leclerc remained in the pits for an extended period to start the session.
He finally emerged after the halfway point in the hour, as his rivals were beginning their qualifying simulations.
Hadjar made an immediate impression as he moaned several times about traffic during the session.
Poised to be promoted into RB next season in place of Liam Lawson or Yuki Tsunoda, whichever takes over from Sergio Perez, it highlighted a concern many hold around his mentality.
There were no such concerns surrounding Doohan who quietly worked through his program and kept out of trouble.
The qualifying simulation runs highlighted what had been seen earlier on the longer runs, with McLaren and Mercedes closely matched at the top.
Ferrari’s pace remained a mystery as, with 15 minutes remaining, Charles Leclerc sat only 10th best.
However, his program was significantly different to his rivals meaning it cannot be compared like-for-like.
His qualifying simulation began with just 10 minutes remaining, offering him a cooler, more rubbered in track.
It was a rapid lap, enough to propel him to the top of the timesheets by two-tenths and suggested Ferrari is in the conversation with McLaren and Mercedes, though exactly which order the three found themselves is less clear.
Again, Red Bull Racing looks half a step back, potentially more given Perez was only 10th at 1.1s off the pace.
While Leclerc topped the session, it wasn’t all roses for the Maranello operation as a battery issue lost him time and will see him take a 10-place grid penalty come the race.
With the Scuderia locked in battle with McLaren for the constructors’ championship, it’s a heavy blow for the Prancing Horse early in the weekend.
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