Miami (AFP) - World championship leader Charles Leclerc was fastest for Ferrari in Friday morning's opening free practice ahead of the inaugural Miami Grand Prix.
The 24-year-old Monegasque clocked a best lap in one minute and 31.098 on soft tyres to outpace nearest rival George Russell, in an updated Mercedes, by 0.071 seconds.World champion Max Verstappen was third for Red Bull.
Russell's team-mate seven-time champion Lewis Hamilton was eighth after gaining a late exemption to keep in his nose stud, following a bling clampdown by the sport.
Mercedes introduced a major package of aerodynamic upgrades and were rewarded with a revival on the track.
Sergio Perez was fourth in the second Red Bull, ahead of Pierre Gasly of Alpha Tauri, Carlos Sainz in the second Ferrari and Alex Albon for Williams.
Behind Hamilton in eighth were Kevin Magnussen, ninth for Haas, and Daniel Ricciardo, 10th for McLaren.
On a near-perfect day of blue skies and sunshine, the session began in hot conditions with an air temperature of 34 degrees and the track at 54, but with fast-forming clouds threatening rain.
The track surface was described as gritty and potentially loose, as the early runners, led by Lance Stroll, began setting lap times and testing their limits on the new track.
Verstappen, pushing hard, skimmed a wall under the bridge at Turn 13 after nine minutes, having gone top, before Leclerc outpaced him, the pair enjoying finding their limits as others spun and slithered.
Leclerc and his Ferrari team-mate Sainz traded fastest laps as they led the way, the Italian team having introduced a revised rear wing, while the Mercedes' duo both lapped in the top ten.
Hamilton had removed most of his jewellery in compliance with a scrutineers' clampdown, which had generated much controversy before the action began.
He kept his nose stud, however, for which he was given a special exemption, according to a pre-session note circulated by the FIA, confirming that Mercedes had finally completed a scrutineering declaration.
This meant both of their drivers would obey the rules about 'the wearing of jewellery' and 'compliant underwear', issues that had annoyed several drivers including four-time world champion Sebastian Vettel.
The Aston Martin driver chose to show his feelings on the subject by wearing his underpants over his race suit as a sign of protest.
Hamilton's exemption was reported to have been granted for two races and came after his successful efforts to remove his earrings.
On track, the first crash of the weekend came after 36 minutes when Valtteri Bottas clattered into the barriers at Turn Seven, prompting a first red flag.
After an eight-minute interruption, the action resumed with Hamilton, making the best of his improved Mercedes, rising to second before Sainz collected a front left puncture and spun at Turn Four.
In a final rush, Verstappen regained brief control at the top of the order and Russell proved Mercedes' rediscovered pace by taking second before Leclerc clocked his best ahead of the Briton.
Hamilton, also on softs, was fast, but slowed by Tsunoda, and wound up eighth.
