Rosberg’s best time of 1m 23.022s, set on soft tyres, put him two-tenths clear of Williams’ Valtteri Bottas - who clocked his best lap on Pirelli’s ultrasoft compound.
It was the first time Mercedes have run the soft rubber, the world champions having used only mediums and hards in last week’s opening test. And it was another busy day for the Silver Arrows, with Rosberg notching up 82 laps in the morning and Lewis Hamilton another 90 as he completed a race simulation in the afternoon.
Fernando Alonso brought out the red flags just before lunch when his McLaren stopped on track, but the team bounced back in the afternoon, with the Spaniard totalling 93 laps en route to a highly encouraging third in the times.
Just behind Alonso was Kimi Raikkonen, who spent much of the afternoon in the Ferrari garage thanks to technical problems, and Red Bull’s Daniil Kvyat who also lost track time thanks to a brake problem which caused a small fire on his RB12.
It was also a frustrating day for newcomers Haas, who were forced to abandon their programme early thanks to a fuel system problem which left Esteban Gutierrez 11th in the times on just 23 laps.
By contrast, Toro Rosso and Force India enjoyed excellent reliability, with Max Verstappen completing a mammoth 144 laps in his newly race-liveried STR11 and Nico Hulkenberg 121 in his VJM09.
They finished seventh and eighth respectively, just ahead of Felipe Nasr who gave Sauber's 2016 machine, the C35, a solid debut as he racked up 103 laps.
Tuesday's unofficial testing times from Barcelona
|1||Nico Rosberg||Mercedes F1 W07 Hybrid||1:23.022||82|
|2||Valtteri Bottas||Williams-Mercedes FW38||1:23.229||0.207||123|
|3||Fernando Alonso||McLaren-Honda MP4-31||1:24.735||1.713||93|
|4||Kimi Raikkonen||Ferrari SF16-H||1:24.836||1.814||72|
|5||Daniil Kvyat||Red Bull Racing-TAG Heuer RB12||1:25.049||2.027||69|
|6||Lewis Hamilton||Mercedes F1 W07 Hybrid||1:25.051||2.029||90|
|7||Max Verstappen||Toro Rosso-Ferrari STR11||1:25.176||2.154||144|
|8||Nico Hulkenberg||Force India-Mercedes VJM09||1:25.336||2.314||121|
|9||Felipe Nasr||Sauber-Ferrari C35||1:25.493||2.471||103|
|10||Kevin Magnussen||Renault R.S.16||1:25.760||2.738||119|
|11||Esteban Gutierrez||Haas-Ferrari VF-16||1:26.661||3.639||23|
|12||Rio Haryanto||Manor Racing-Ferrari MRT05||1:27.625||4.603||45|