The German, who won Sunday's Formula 1 Gran Premio de Espana Pirelli 2015, set a best time of 1m 24.374s - quicker than his pole time on Saturday - which left him more than two seconds clear of the field. Rosberg also racked up an imperious 146 laps, comfortably more than any other driver achieved.
“The track was a little bit quicker than over the race weekend and we did many laps, so I’m a bit tired!" said Rosberg. "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. 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.”
Ferrari protegee and GP2 racer Raffaele Marciello had put the Scuderia second at lunch, but was displaced as Sauber's Marcus Ericsson improved in the afternoon. Just 0.024s split the pair at the day's conclusion.
Marciello was still able to take third, and also worked his way into triple figures in the lap count - his eventual tally of 125 was bettered only by Rosberg and Pierre Gasly at Toro Rosso. He will take over from Ericsson at Sauber for the second and final day tomorrow.
“Even though it’s the first time I have driven this car, I got positive feelings from it,” said the Italian. “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.”
Daniil Kvyat finished fractions of a second down the road in fourth for Red Bull, as the team recovered from a quiet morning - the Russian completed just 20 laps - to break into triple figures by the day's close. Pastor Maldonado rounded out the top five as Lotus tested various new parts and set-up configurations.
Having been drafted in a day early in place of the ill Pascal Wehrlein, Briton Nick Yelloly enjoyed an extremely productive F1 debut as he racked up 109 laps and secured sixth overall in Force India's VJM08.
“It’s always enjoyable seeing a young driver get to grips with a Formula One car for the first time,” commented Force India’s chief race engineer Tom McCullough. “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.”
Gasly, like Yelloly making his F1 debut in the test, was seventh in the STR10. Unsurprisingly the young Frenchman, who will jump across into Red Bull's RB11 on Wednesday, said it had been a “wonderful day”.
“This morning, getting into a Formula One car for the first time was something special,” he said. “The feeling you get from the car is unbelievable. Everything is almost perfect, with elements like the power steering for example and of course there’s much more power than in the other formulas and you have more grip too.
“I really enjoyed the experience and I made the most of it, doing a lot of laps. All drivers dream of driving a Formula One car and having now done it, I am even more determined to reach my goal of racing in this category. It was awesome and I can’t wait to try it again.”
Felipe Massa completed the fewest laps of the day - 54 - as Williams registered a low-key eighth. The team focused on tyre degradation, as well as on development work for this and next year’s car.
That left Oliver Turvey to prop up the timesheets in the McLaren MP4-30, the Woking squad focusing on aerodynamic and suspension analysis following a difficult weekend in Spain, which included Jenson Button describing the car's handling as "pretty scary".
Williams development driver Alex Lynn, Ferrari's reserve Esteban Gutierrez and Mercedes-backed Esteban Ocon will be among the new faces on the second and final day of testing on Wednesday.
Unofficial Tuesday testing times from Barcelona