Nico Rosberg set the pace on the opening day of the first in-season test of 2014 as Mercedes enjoyed more productive running.
With the test taking place in Bahrain following Sunday's race, Rosberg completed 121 laps and set a fastest time of 1:35.697 to lead Nico Hulkenberg by just over 0.3s. Hulkenberg improved during a late run in the morning but was not completely happy with the steering in his Force India and only completed 25 laps before lunch, adding another 44 in the afternoon and setting his best time on the soft tyre.
Fernando Alonso was third quickest for Ferrari but almost a second shy of Rosberg's time. Alonso was limited to 69 laps as he caused the first red flag of the day when he stopped at Turn 2, pulling his Ferrari across to the inside of the circuit, but was able to return to the track before lunch.
Kevin Magnussen was fourth quickest for McLaren but his day was not without its problems. His morning came to a premature end, with Magnussen changing out of his overalls and debriefing with his engineers despite there being over 45 minutes until the lunch break.
With McLaren running new suspension components, the team got in some substantial mileage in the afternoon to end the day with 102 laps.
Valtteri Bottas was over 1.6s off the pace for Williams and only completed 28 laps before his day was halted early in the afternoon. However, the team was confident it had managed to complete its aerodynamic programme in that time and will test tyres for Pirelli alongside Mercedes on Wednesday.
Max Chilton got within two seconds of Rosberg's time with a late lap for Marussia having been hampered by a hydraulic problem which stopped him at Turn 4 before the lunch break.
Daniel Ricciardo didn't emerge in the first hour due to technical issues and completed just one lap before 11am, but ended up with the seventh fastest time – 2.6s off the pace – having completed 91 laps as Red Bull attempts to use the test to claw back some of the early Mercedes' advantage. Ricciardo was the subject of a strange incident in the afternoon though when he had to cut a run short having hit a bird.
Sergey Sirotkin made his testing debut for Sauber and managed 75 laps with a best time 3.3s slower than Rosberg. He will hand over to Giedo van der Garde tomorrow, with Sauber the only team to not run at least one race driver this week.
Caterham was carrying out tyre testing for Pirelli on the opening day and Robin Frijns completed 63 laps in the morning as part of the programme, while most of the other teams were working on aerodynamic analysis. However, a hydraulic issue meant he was unable to return to the track in the afternoon.
It was another tough day for Lotus as Pastor Maldonado completed just 16 laps, with power unit issues once again to blame.