Sergio Perez underlined the belief that Red Bull are favourites for the 2023 championship in first practice at the season-opening Bahrain Grand Prix.
The Mexican was 0.438 seconds quicker than the impressive Aston Martin of Fernando Alonso, with world champion Max Verstappen in third place.
Verstappen, apparently struggling with a lack of front-end grip, was 0.617secs behind his team-mate.
McLaren’s Lando Norris was fourth and Lewis Hamilton 10th for Mercedes.
Red Bull team principal Christian Horner said conditions had changed since pre-season testing week and “it is just a matter of tuning the set-up for the track”.
Norris’ position was a surprise – McLaren have admitted that they have failed to meet their development targets and expect a slow start to the season – although the Briton was 1.407secs off the pace.
Ferrari’s Charles Leclerc was fifth quickest after a session affected by problems with his rear wing.
A new design was flexing on several axes out on track and had to be removed and replaced with the same version fitted to team-mate Carlos Sainz’s car.
Team principal Frederic Vasseur said the wing was a test item that did not work as intended. It will not be run again this weekend but would “be back soon”.
Spaniard Sainz had a high-speed spin at Turns Nine and 10 midway through the session and was slowest of all.
McLaren rookie Oscar Piastri also had a spin, his coming through the fast corners of Turns Six and Seven. The Australian finished his session 12th fastest.
Aston Martin’s Lance Stroll was sixth quickest despite this being his first experience of his new car after begin forced to miss pre-season testing last week with a wrist injury sustained after a cycling accident.
Haas driver Kevin Magnussen, Alfa Romeo’s Zhou Guanyu and Valtteri Bottas and Hamilton completed the top 10, with the second Mercedes driver George Russell 11th.
Mercedes and Leclerc did not run the soft tyre, which everyone else in the top 10 used to set their times.
The second session, held at twilight and therefore more representative of conditions for qualifying and race, starts at 18:00 local time (15:00 GMT).
