Leclerc posted a lap that was just 0.079s quicker than Sainz’s with a 1m19.828s to edge out his teammate and head the timing sheets during the first hour of running at Barcelona on Friday. 

Red Bull’s Max Verstappen was third, 0.336s down on the benchmark set by his main title rival, who the Dutchman trails by 19 points after the opening five rounds. 

George Russell was fourth-fastest, over seven-tenths off the pace, as Mercedes trailed its first major upgrade package of the season. 

Behind Russell was Fernando Alonso, who ended up splitting the Mercedes drivers as he jumped ahead of Lewis Hamilton into fifth with a late improvement. 

But the Alpine driver faces an investigation for impeding the seven-time world champion during the opening practice session. 

The rest of the top-10 was completed by the McLaren and Toro Rosso drivers, with Lando Norris leading Pierre Gasly, teammate Daniel Ricciardo and Yuki Tsunoda. 

Three regular drivers sat out of FP1 as Robert Kubica returned to action for Alfa Romeo in place of F1 rookie Guanyu Zhou, while two rookies completed the first of two mandatory appearances this year. 

Formula E champion Nyck de Vries finished 18th-fastest for Williams, managing a time that was a tenth better than Nicholas Latifi on an impressive first outing on a grand prix weekend. 

Also making his FP1 debut was Red Bull junior Juri Vips, who ended up slowest of all and four seconds slower than Max Verstappen in the other Red Bull.