Austin, Texax: Carlos Sainz outpaced newly-acclaimed double world champion Max Verstappen to top the times for Ferrari in Friday morning's opening free practice at the United States Grand Prix.
The Spaniard clocked a best lap in one minute and 36.857 seconds to beat Red Bull's Dutchman by 0.224 seconds with seven-time champion Lewis Hamilton third for Mercedes, 0.475 seconds adrift.
Lance Stroll was fourth for a revived Aston Martin ahead of Red Bull's Sergio Perez, two-time champion Fernando Alonso of Alpine and George Russell of Mercedes.
Pierre Gasly was eighth for Alpha Tauri ahead of Lando Norris of McLaren and four-time champion Sebatian Vettel, who was 10th for Aston Martin in a session that was largely uneventful as the teams explored the conditions.
The session began in bright and dry conditions with a perfect blue sky overhead and Hollywood film star Brad Pitt in the pitlane as the Alpha Tauri and Aston Martin teams led the way.
Perez set the early pace, but most attention in the paddock remained focussed on Red Bull's ongoing "silent" negotiations with the FIA over an "Accepted Breach Agreement" to settle the team's breach of the sport's cost cap last year.
An anticipated news conference ahead of practice had been cancelled, leaving the focus to switch to the introduction of five guest test drivers in opening practice with Ferrari, McLaren, Williams, Alfa Romeo and Haas.
One was Antonio Giovinazzi in Kevin Magnussen's Haas car, but his session ended early when he spun at turn six, causing a brief red flag. The Italian's dream of an F1 comeback may have ended too, handing impetus to Mick Schumacher's bid to retain his seat.
The other "rookies" included Russian Robert Shwartzman replacing Charles Leclerc, Spaniard Alex Palou in for Daniel Ricciardo, American Logan Sargeant in Nicholas Latifi's car and Frenchman Theo Pourchaire replacing Valtteri Bottas.
Verstappen soon stamped his authority on proceedings after 18 minutes by going top on his first flying lap in 1:38.272, clear of Ocon by half a second. The champion trimmed that three minutes later as Perez moved up to second.
The Mexican, facing a grid penalty for taking a new engine, was soon overhauled by Sainz who split the Red Bulls before Alonso, Vettel and Hamilton also enjoyed spells in second.
As the conditions improved, many drivers began to push and deliver spectacular car management, the impressive Stroll firing himself top ahead of Verstappen after 42 minutes before being eclipsed by Sainz in 1:36.857.
Hamilton, a five-time winner in Austin, demonstrated his affinity with the track by moving up to second, but nearly half a second off the Spaniard's pace with 12 minutes remaining.
Verstappen who had slipped to fifth rose to second, two-tenths off Sainz, with five minutes to go, despite an imperfect lap shortly before Vettel rescued his car from a major slide at Turn Seven.
"There must be something wrong with the car because I have no front end in low speed," complained the Dutchman, who hopes to clinch Red Bull's first constructors' title since 2013 this weekend.