Ferrari again proved to be the Silver Arrows’ nearest threat, with Sebastian Vettel and Kimi Raikkonen third and fourth respectively, ahead of the impressive Toro Rossos of rookies Carlos Sainz and Max Verstappen.
It was a good session for the three test drivers in action, with Raffaele Marciello 12th for Sauber, immediately followed by Jolyon Palmer for Lotus, and Susie Wolff - enjoying her first 2015 outing - for Williams.
It is early days of course, but the early indications suggest there could be some incredibly close battles among the field. On top of Rosberg edging Hamilton, 1m 26.828s against 1m 26.898s, Vettel and Raikkonen were covered by just 0.026s, 1m 27.806s to 1m 27.832s respectively.
Neither team were completely happy. At Mercedes, Rosberg had an off at Turn 10 and Hamilton complained of understeer; at Ferrari, Vettel went off in Turn 1 and again in Turn 10, while Raikkonen was angry when he got sent out straight into traffic at the end. Rosberg was also summoned to report to the stewards for a breach of pit lane entry protocols.
Sainz was the fastest home driver, taking fifth ahead of Toro Rosso team mate Verstappen, with 1m 28.132s to 1m 28.529s, ahead of Daniil Kvyat on 1m 28.785s for Red Bull. All of this was mild encouragement for the Renault runners, but Daniel Ricciardo lost virtually the whole session with a suspected throttle problem at full revs on his Renault motor. The Australian got going again right at the end and did a fine job to lap in 1m 29.075s to hoist himself from last to ninth, behind Felipe Massa who lapped his Williams in 1m 28.831s.
Felipe Nasr rounded out the top 10 for Sauber with 1m 29.140s, chased by Force India's Nico Hulkenberg on 1m 29.409s. Then came the three subs - Marciello took Marcus Ericsson's Sauber round in 1m 29.630s for 11th ahead of Palmer in Romain Grosjean's Lotus on 1m 29.676s and Wolff in Valtteri Bottas' Williams on 1m 29.708s. Solid jobs from all of them.
Fernando Alonso survived a quick 360 degree spin in Turn 12 right at the end to take 15th in the newly-liveried McLaren, with 1m 29.813s. Team mate Jenson Button, unhappy with the power delivery on his engine, was right on his tail with 1m 29.817s.
Sergio Perez had a difficult morning and was 17th on 1m 30.096s in the second Force India, while Pastor Maldonado was one spot lower in the second Lotus after suffering problems late in the session which restricted him to 1m 30.110s.
The Marussias rounded out the timesheet, with Will Stevens and Robert Merhi well matched on 1m 32.471s and 1m 32.647s.