Max Verstappen led Red Bull team-mate Daniel Ricciardo in opening practice for the season-closing Abu Dhabi Grand Prix.
The Dutchman finished 0.454 seconds clear of Ricciardo at the sun-drenched Yas Marina circuit, with the Mercedes pair of Valtteri Bottas and Lewis Hamilton third and fourth respectively.
Hamilton, who is sporting a gold crash helmet this weekend, and the number one on his Mercedes to celebrate his fifth world championship, finished one second off the pace.
The Formula One circus is in the Middle East this weekend for the final stop of the 21-race calendar.
Hamilton, 33, sealed the title with two rounds to spare, and asked permission to change the number 44 on his Silver Arrows to number 1.
It marks the first time the number, traditionally reserved for the world champion, has been on the grid in four years.
The world champion was significantly slower than the Red Bull of Verstappen in the opening running, but the second practice session which takes place later on Friday will be more representative of the conditions for qualifying on Saturday, and the race, too.
Indeed, Sebastian Vettel finished a distant eighth for Ferrari, two seconds down on Verstappen, with team-mate Kimi Raikkonen, taking part in his final race for Ferrari, one place better off.
Fernando Alonso will bring the curtain down on his F1 career here on Sunday after 17 years, and the double world champion finished 19th of the 20 runners, nearly four seconds off the pace.
Robert Kubica, confirmed as a Williams driver for next season to complete his remarkable comeback from an horrific rally crash almost eight years ago, finished last.
The crash-prone Marcus Ericsson was in the wars again after he lost control of his Sauber on the exit of Turn 1, and slid across the track and into the barriers. He limped back to the pits with a damaged front wing.
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