Sergio Perez was quickest for Red Bull in the opening practice of the new Formula One season in Bahrain.
The Mexican driver finished the first one-hour session ahead of Fernando Alonso for new team Aston Martin, with world champion Max Verstappen third. Lewis Hamilton was only 10th for Mercedes, more than two seconds off the pace.
Red Bull head into the first round of the season expected to deliver Verstappen a hat-trick of titles.
And the world champions appear primed to build on their ominous pre-season form with Perez leading the way in Bahrain, four tenths clear of Alonso.
Double world champion Alonso, 41, is making his debut for Aston Martin following his switch from Alpine.
The British-based team have endured two underwhelming seasons back in F1, but they have taken great strides over the winter and their encouraging form continued here with Alonso splitting the Red Bull cars.
Hamilton is gearing up for this 17th season in F1 after last year failing to win a race for the first time in his career.
The seven-time world champion and his Mercedes team will have been desperate to bridge the gap to Red Bull.
But Hamilton admitted here on Thursday that his machine is not where it needs to be – and while times in practice have to be treated with caution as the teams trial different strategies and fuel loads – there could be cause for concern at the Silver Arrows, with George Russell 11th, one place behind his team-mate.
Elsewhere, Lando Norris finished fourth in his McLaren, one place clear of Ferrari’s Charles Leclerc.
He finished sixth, one second slower than Alonso in the other Aston Martin.
Second practice starts at 1800 local time (3pm UK).