Just 48-hours after winning the Spanish Grand Prix, Nico Rosberg returned to the Circuit de Catalunya where he topped the timesheets on the first day of in-season testing.

The German completed 146 laps on his way to posting a best time of 1:24.374, 0.307s quicker than his pole-winning time last Saturday.

With Manor opting to miss the two-day test, nine drivers were on duty, though Force India had to call on the services of Nick Yelloly when Pascal Wehrlein 'called in sick'.

For the world champions, today's schedule consisted of set-up work ahead of the Monaco Grand Prix, in addition to the evaluation of a number of new parts. Rosberg completed 78 laps before the lunch break, and a further 68 in the afternoon.

"Today was a great test day for sure," he said. "The track was a little bit quicker than over the race weekend and we did many laps, so I'm a bit tired! But it's my only test during the season so it's important. Today, we tested a lot of different things - some more generally for the rest of the season and some for the next race.

"Monaco has very unique setup characteristics so we evaluated a few of those," he added. "The last sector here has a lot of tight corners - so it's like Monaco in a way, which is useful. The car felt very good there so I'm feeling optimistic and ready for the next race. It's in my home town, it's a legendary circuit and it should be a good weekend so I'm really looking forward to it.

Marcus Ericsson was back in the C34-Ferrari as Sauber focussed on a full programme of aerodynamic measurements as well as work on the tyres and set-up for the next races. In total the Swede completed 98 laps.

"I am happy," said Ericsson. "Today was very productive as we went through the planned programme. After the lunch break we were able to run trouble-free and I completed almost a hundred laps. We gathered a lot of information, driving on different tyre compounds. This was very encouraging for the next race and the future."

"It was a good day for us," insisted Test Engineer, Paul Russell. "Marcus was quite happy with the results. We were able to go through a list of things that could not be done during a race weekend. Now we have to analyse our data and prepare for the test tomorrow."

Under fire from the Italian media for not running either of its race drivers in the test, Ferrari, which has reserve Esteban Gutierrez on duty tomorrow, today ran Raffaele Marciello.

The Italian posted the third best time of the day as the Italian team concentrated on aero testing and set-up work.

"Even though it's the first time I have driven this car, I got positive feelings from it," he said, "as it has a lot of grip compared to the GP2 cars that I'm used to driving.

"I think the team has done a good job: the last time I did a test, it was in Abu Dhabi last year and there's definitely been a lot of progress made since then. We will now analyse the large quantity of data we gathered on the new aerodynamic package used last Sunday to further improve our performance.

"For me, it was a nice feeling to get into a Ferrari, especially as an Italian, but you must always keep your feet on the ground and concentrate on what you are doing."

Daniil Kvyat was back in the RB11 completing 101 laps, despite his programme being delayed in the morning while his crew carried out work on the gearbox. After the covers were back on, he was able to recover the lost time and complete his run plan, passing the 100-lap mark shortly before the chequered flag.

"Overall it was a very positive day - the work got done," said the Russian. "We lost a couple of hours in the morning but had a really strong afternoon and managed to recover most of the programme - which was very important.

"We are limited in what we can test on a Friday at a race meeting so these sessions are very important to us. They're crucial in helping us understand how the car is working, and for gathering as much information as possible. What we learned today will help us progress."

"Once the car was ready the programme went really well and we had a good, solid day of testing," said Head of Race Engineering, Guillaume Rocquelin. "We concentrated on suspension and aerodynamic work, changing car parameters and trying different things. We brought some new parts to the Spanish Grand Prix race weekend and today we were able to test those in more detail."

Lotus' test got underway with Pastor Maldonado on driving duties, the Venezuelan having been retired from Sunday's race following damage to his rear wing. The Enstone team enjoyed a full and productive morning, but ran less in the afternoon due to a loss of power requiring a precautionary end to the day's running in order to replace the fuel system.

"The car was in good shape and we ran through a lot of our programme in the morning," said Maldonado. "We made strong progress with some positive conclusions about the parts we ran which is encouraging for the future. Track conditions today were better than in the race here two days ago in terms of the wind and level of grip which was beneficial to us. We did do some work for the next race in Monaco so we hope to be fighting strongly there."

"We enjoyed a productive morning in very hot conditions and were able to run though a significant number of tests of new parts as well as configurations of parts and different set-ups, all of which has been very promising," added Alan Permane. "Our running in the afternoon was curtailed somewhat as we stopped running early as a precautionary measure to replace the fuel system ahead of tomorrow's running, but it has still been a positive day."

Nick Yelloly (pictured) has been working on Force India's simulator programme since 2014 and therefore a priority of the day was to make comparisons between the real car and the simulator. The job list also included a comprehensive aero programme with various measurement tools fitted to the VJM08 throughout the day.

"It felt really good to finally get my chance in a Formula One car," said Yelloly. "I've been working towards this day for a long time and I need to say a big 'thank you' to everyone at Sahara Force India for giving me this opportunity. The first few laps felt a bit unusual, but I soon got comfortable in the car.

"One of the first things I noticed was the directness of the power steering compared to a GP2 car because you only have to put a slight input and the car responds immediately. The set-up was pretty much where we needed it straight away and we just chipped away at it making a few small adjustments during the day.

"The main focus was on aero and we did a big sweep in the morning, but I also got the chance to run on soft tyres in the afternoon. I'm feeling really positive about the day and I hope it's been useful for the team."

"It's always enjoyable seeing a young driver get to grips with a Formula One car for the first time," admitted Tom McCullough, the team's Chief Race Engineer. "Nick was clearly excited about the opportunity, but he was very mature with his approach and he impressed the team with his feedback. He didn't put a foot wrong all day and helped us gather a lot of very useful data.

"Our main focus was to gather pressure tapping data with various rakes and hardware fitted to the car. Nick's extensive experience on our simulator helped him get up-to-speed quickly and ensured we completed a rather ambitious job list. Nick's experience in the VJM08 today will be invaluable as we continue to develop our simulator back at base."