Lewis Hamilton was the fastest driver in the second session of free practice on Thursday in Bahrain, followed by team-mate George Russell as Mercedes looked strong on the first day of the season proper.
Max Verstappen set the sixth fastest time, behind an Aston Martin, McLaren and Ferrari, as questions were raised over the Red Bull star's fuel load and engine settings.
Daniel Ricciardo topped the timesheets in FP1, with the VCARBs and McLarens filling the top four slots as Verstappen set just the sixth fastest time of the session again.
The first race 'weekend' of the season got underway on Thursday morning, with high winds and chilly temperatures providing tricky conditions for the grid.
Verstappen continued his 2023 form for complaining about his car, telling his garage that 'everything is s***' after setting the fastest lap of the first set of runs, before mithering over the feel of the car on upshifts and downshifts.
The times from the early session aren't expected to be representative of the qualifying order for Friday evening, with different track conditions and teams still looking to key their cars into the circuit - but the second session should be more of a balanced showing.
The only small moment of technical drama came right at the start of the first session, Zhou Guanyu limping into the pits after complaining to his engineers that his brakes 'didn't work', but he quickly got back on track.