Max Verstappen was fastest in the opening session of the Saudi Arabian Grand Prix ahead of Sergio Perez and Fernando Alonso.
The Dutchman returned to the circuit on Friday morning after missing out on Thursday due to a stomach bug.
After a few minutes in the garage, he immediately appeared to set the pace on the Soft tyre by going 0.015s quicker than the early lap set by Alonso.
On his second push lap he went a further 0.500s faster than Alonso, while teammate Perez was 0.777s off the pace.
A late run by Perez on the evolved track enabled him to improve on his lap by a couple of tenths in the closing stages to put him second quickest.
Alonso's teammate Lance Stroll managed to get up to fourth fastest after struggling with traffic on his early runs.
Mercedes a second off the pace
Both Mercedes were a second off the pace from Verstappen on the Soft tyre, with George Russell leading Lewis Hamilton.
Hamilton complained of poor grip during his timed laps on the Soft, electing to switch to the Hard tyre towards the end of the session.
Alex Albon continued to show Williams' straight-line pace by going eighth fastest, matching Verstappen in the speed trap by going 304kph.
A late improvement from Pierre Gasly put him seventh quickest, although the Alpine driver was complaining about the brake performance during his lap.
Ferrari elected to run higher fuel runs midway through the session with both cars on the Soft tyre.
Carlos Sainz was the quicker of the two Ferrari's with a time that was 1.1s off the best set by Verstappen for sixth fastest, while Charles Leclerc was eleventh fastest on a weekend that he takes a 10-place grid penalty.
Result Free practice 1 - Saudi Arabian
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F1 2023 Saudi Arabian Grand Prix RN365 News dossier
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