Just 48-hours after its total domination of the Bahrain Grand Prix, Mercedes was back in action at Sakhir leading the way in the first in-season test of the year.

Nico Rosberg, who finished second to teammate Lewis Hamilton as the German team scored its second successive 1-2, topped the timesheets today as well as completing the most laps.

For the Brackley-based squad, today's programme consisted of running through numerous set-up evaluations. Rosberg emerged for his first run at 09:15, completing 70 laps in the morning before completing a further 51 laps in the afternoon, as the team continued running right up to the chequered flag at 17:30.

Between them, Mercedes-Benz power units, which filled six of the first eight positions on Sunday, completed a total of 1,732 km today.

"Our main aim today was to try different directions with set-up and to get to know the tyres a bit better," said Rosberg. "You never stop learning how to get the best out of the tyres, so it has been a productive day from that perspective. We also did a bit of work on the brakes as this is an area I'm not one hundred percent happy with at the moment.

"We've had a good few weeks on track but you are never at the maximum level of performance," he insisted. "There is always more to be found and we are constantly pushing to improve the car and also ourselves as drivers. Having said that, the team are doing a fantastic job with this car from every perspective. Reliability, car performance, Power Unit performance: it's all there and it's a pleasure to be a part of a team with such positive momentum."

Having taken the third podium spot - the best that is currently on offer as far as the opposition is concerned - Force India maintained its form, Nico Hulkenberg completing 69 laps on his way to posting a best time just 0.367s off Rosberg's best.

Concerned at his team's start to the season, particularly last weekend when it could only manage ninth and tenth, Fernando Alonso is on duty for both days of the test.

In the morning, the Spaniard concentrated on fine tuning various electronic configurations and on taking aerodynamic measurements with constant speed runs down the main straight. In the afternoon, work was carried out in short runs, lapping to evaluate different set-up choices.

Running numerous odd-looking sensor devices over the course of the day, the Maranello outfit was the cause of a red flag period when Alonso stopped on trach mid-morning.

As previously reported, in the interests of driver continuity, McLaren changed its line-up, giving Kevin Magnussen both days in the car as opposed to the original plan which would have seen Oliver Turvey test today and Bahrain GP2 Feature Race winner Stoffel Vandoorne driving the car on Wednesday.

With the in-season tests focused primarily on mileage, reliability running and component validation, the Woking outfit took the opportunity to undertake in-depth analysis in order to broaden its understanding of MP4-29.

Despite making some lengthy set-up changes to the car between runs, Magnussen managed to complete 102 laps and post a best time 0.937s off Rosberg's pace without problem.

While Valtteri Bottas finished the day fifth quickest, the Finn only completed 28 laps over the course of the day, however, the Grove outfit says it is pleased with the day's results.

"We had good mix of tests today with aero, mechanical, car set-up, electronics and power unit, and we managed to get through everything which is hugely encouraging," said Rob Smedley. "The results were very positive and we collected a lot of good data, which is good news. Valtteri also did a good job for us today. We are pleased to be running here as it has given us that chance to build on the data from the weekend and means we have continued development from the start of the race weekend. Felipe Nasr will be in the car for us tomorrow as we complete a 2015 tyre test programme for Pirelli."

"Overall it was a good day as we managed to complete the programme as planned," said Bottas. "We then worked on set-up and we were quite experimental, so hopefully that will help in the next few races. Next it was time to test some new aero components with some positive results. The track conditions were different from the race, but actually better for testing as there was less wind.