Valtteri Bottas set the fastest time of the morning session of testing in Abu Dhabi while McLaren failed to run the new Honda power unit.
Bottas set a best time of 1:43.884 to finish the session on top, over 1.2s clear of Nico Rosberg in the Mercedes. The team said Rosberg - who was back in the car after missing out on the world championship less than 48 hours earlier - would be carrying out aerodynamic and tyre tests.
McLaren was set to test the new Honda power unit but Stoffel Vandoorne never left the garage in the opening four hours of running, with racing director Eric Boullier explaining an electrical issue was to blame
Kimi Raikkonen was third fastest for Ferrari, setting a time of 1:46.016 late in the session. Ferrari also had Raikkonen's 2015 team-mate Sebastian Vettel in the garage as he cast his eye on the team's testing program.
Carlos Sainz Jr was fourth quickest for Red Bull ahead of Marcus Ericsson who was getting his first running in the Sauber having been announced as one of the team's race drivers for 2015. Will Stevens - who took Ericsson's seat at Caterham for the final race of the season - was sixth fastest and completed 50 laps by lunchtime.
Jolyon Palmer's F1 debut didn't go so smoothly at Force India as he completed just 18 laps before an engine issue caused him to stop out on track. Palmer's stoppage at Turn 13 brought out the second red flag of the day, with Max Verstappen crashing at Turn 19 early on due to a front suspension issue.
Verstappen did return to the track briefly before lunch but is yet to set a time.