Red Bull's double world champion Max Verstappen was fastest, with Fernando Alonso close behind for Aston Martin, as Formula One started three days of pre-season testing in Bahrain on Thursday (Feb 23).The Dutch 25-year-old was top of the timesheets before and after lunch at Sakhir as teams mainly focused on aerodynamics with prominent rakes attached to the cars in their first proper running.Verstappen won 15 of 22 grands prix last year and will be chasing his third straight title when the 23-race season starts on Mar 5."We had a good day today, we completed a lot of laps which is what we wanted - almost three grand prix's worth," he said. "It was also a smooth day; we barely had any issues and we could really focus on the car and try a few things."It’s nice to see how the car has evolved from last year."Ferrari's Carlos Sainz was second in the morning, 0.294 slower but on top for a majority of the session, with Williams Alexander Albon third and doing the most laps (74).Double world champion Alonso was soon up to speed at his new team in the later session, 0.029 slower than Verstappen who clocked a best of one minute 32.837 seconds and did 157 laps as the only driver to be testing all day.Mercedes and Ferrari also sounded positive, with Mercedes boss Toto Wolff noting a buzz of excitement in the garages.The Austrian said it had been a productive day and very different from 2022 when the team were wrestling with a bouncing, "porpoising" car.The former champions had George Russell in action for the opening stint, with the Briton queuing up in the pitlane to be first out, before seven-times world champion Lewis Hamilton hit the track later on."He was generally happy with the car.