Lewis Hamilton opened his bid for an unprecedented eighth world championship by finishing fourth in first practice for Sunday's Bahrain Grand Prix.
As Formula One roared back into life here in the Gulf Kingdom, Max Verstappen delivered on Red Bull's encouraging pre-season form by ending the one-hour running quickest.
The impressive Dutchman finished three tenths faster than Valtteri Bottas, with Hamilton half-a-second off the pace. British driver Lando Norris split the Mercedes duo in third.
On the eve of the new campaign, Hamilton, 36, said his all-conquering Mercedes team were no longer the fastest on the grid.
And judging on the very early evidence of the first running in Bahrain's searing heat, it appears as though Hamilton will not have it all his own way this year.
Red Bull have been slow out of the gates in recent seasons, but Verstappen posted the fastest time of the winter test and again finished top of the charts here. His new team-mate Sergio Perez was sixth.
There were promising signs for McLaren, too. The British team finished third in last year's constructors' championship and Norris, now in his third season in F1, put his McLaren in the mix by clocking a quicker time than Hamilton.
Ferrari endured their worst campaign in four decades last year. Charles Leclerc, now the team's number one talent following Sebastian Vettel's transfer to Aston Martin, was fifth, 0.599 sec behind Verstappen.
Four-time world champion Vettel ended the opening running in 12th for his new team – the Aston Martin name back in F1 following 61 years away – while Fernando Alonso, returning to the grid after a two-season hiatus, was only 16th for the rebranded Alpine team.
On his debut, Mick Schumacher, the son-of seven-time world champion Michael Schumacher, finished last but one of the 20 runners with his Haas team-mate, another rookie, Nikita Mazepin, bringing up the rear.
The concluding action of the day will take place later on Friday, and will be more representative of the conditions for Saturday's qualifying and Sunday's race, with both taking place at dusk.
