Rosberg's time of 1:22.616 was just 0.007s quicker than the Lotus E21 of Kimi Raikkonen.
Both Rosberg and Raikkonen jumped to the top of the leaderboard after fitting the medium compound tyre during the final hour of running.
Rosberg's morning had been disrupted by checks to his gearbox but he nonetheless edged out Raikkonen.
After electing to skip the opening test, Fernando Alonso was given his first taste of the Ferrari F138 and he finished in third place, the only man to complete over 100 laps.
Reigning world champion Sebastian Vettel topped the morning but despite improving his lap time and becoming the first man to break into the 1.22s, he ended the day in fourth place.
Pastor Maldonado and Valtteri Bottas unveiled the Williams FW35 in the pits prior to the start of testing. Maldonado promptly gave the FW35 its track début and ended the day in fifth place.
The only red flags of the day were caused by Esteban Gutierrez and Charles Pic. The Sauber driver stopped as part of a planned fuel run early in the morning, while Pic caused a red flag in the afternoon when his Caterham came to a halt.
|1||N. Rosberg||Mercedes W04||1:22.616||54|
|2||K. Raikkonen||Lotus E21||1:22.623||40|
|3||F. Alonso||Ferrari F138||1:22.952||106|
|4||S. Vettel||Red Bull RB9||1:22.965||65|
|5||P. Maldonado||Williams FW35||1:23.733||81|
|6||D. Ricciardo||Toro Rosso STR8||1:23.884||68|
|7||S. Perez||McLaren MP4-28||1:24.124||71|
|8||P. di Resta||Force India VJM06||1:24.144||78|
|9||E. Gutierrez||Sauber C32||1:25.124||63|
|10||M. Chilton||Marussia MR02||1:26.747||65|
|11||C. Pic||Caterham CT03||1:27.534||49|