On a rain-hit day in Barcelona, the German was able to gain experience of PirelliÃ¢â‚¬â„¢s intermediate tyres in the morning, before switching to slicks as the team worked through a number of set-up comparisons.
His quickest time of 1:23.168 came during a series of qualifying simulations late in the afternoon, which included use of KERS and the adjustable rear wing.
Vitaly Petrov was second for Renault, with his quickest time just three tenths slower than Rosberg. The Russian was able to complete over 90 laps running through a set-up programme, and changes to front and rear suspension, before making tyre comparisons.
Lewis Hamilton was almost seven tenths slower than Rosberg with a 1:23.858 as McLaren looked to overcome recent reliability issues, but the 2008 world champion had to abandon several runs in the morning.
With the problems fixed, Hamilton was able to set quick times towards the end of the morning session, before going third in the dry conditions in the afternoon during qualifying simulations. He eventually completed 93 laps as McLaren slowed the pace and worked on aero-mapping.
Pastor Maldonado endured a frustrating day, spinning his car in the early wet conditions, while an alternator problem on the FW33 later in the morning also limited running.
Red Bull’s Mark Webber went further than any other driver with 139 laps in the RB7. His quickest time, a 1:24.995, came on the first lap following a tyre change, while in the middle of a race simulation.
Jarno Trulli was hampered by a lack of spare parts for the T128 as Team Lotus experienced further problems with a water leak from a cracked pipe.
The team were however able to give the Italian a decent run in dry conditions in the afternoon with his quickest time of 1:25.454 coming on lap 45 of 48. Trulli also got his first experience of PirelliÃ¢â‚¬â„¢s wet and intermediate tyres in the morning.
Sergio PÃƒÂ©rez completed 115 laps for Sauber, like most teams exploring options with the wet and intermediate tyres, before running a race simulation in the afternoon on the hard and medium compounds to lap within a tenth of Trulli before a rear wing problem ended his day.
Adrian Sutil covered over 100 laps as he continued work on set-up programmes and the adjustable rear wing on the VJM04, setting a quickest lap of 1:25.720 as Force India improved the carÃ¢â‚¬â„¢s balance.
Toro Rosso opted to split their day with reserve driver Daniel Ricciardo taking the morning sessionÃ¢â‚¬â€his last opportunity before the first race practice session of the seasonÃ¢â‚¬â€before SÃƒÂ©bastien Buemi took over in the afternoon.
The Swiss driver completed just 32 laps with limited runs on two sets of slicks, leaving him with more options for the final day of testing on Monday as he finished four tenths slower than Sutil.
Felipe Massa had an eventful day in the Ferrari F150th Italia, twice causing a red flag in the morning when running on intermediate tyres, while his afternoon consisted of a full race simulation with a view to making the tyres last as long as possible without ever really looking to set a quick time, leaving him tenth quickest with a time of 1:26.508.
Timo Glock added mileage to the MVR-02 for Virgin Racing on his way to 11th quickest with a time of 1:26.598 as he also experienced the full range of Pirelli compounds, first in the morning with wet and inters, and then slicks in the afternoon.
Giorgio Mondini enjoyed his first run-out for Hispania as another driver under evaluation by the Spanish team, after Tonio Liuzzi had a similar test on Saturday.
The Swiss driver, who was MidlandÃ¢â‚¬â„¢s third driver for part of the 2006 season, was a credible 12th quickest, 2.5s ahead of HispaniaÃ¢â‚¬â„¢s only confirmed driver for 2011, and only 1.6s slower than Glock.
Daniel RicciardoÃ¢â‚¬â„¢s quickest time was 1:28.329 on slicks on the drying track towards the end of the morning, only finishing some five seconds off RosbergÃ¢â‚¬â„¢s quickest time set in the afternoon.
His lowly position is a result of no running in dry conditions, but the decision to make an early switch of tyres will help Toro Rosso with vital data on the crossover period between compounds.
Like Ricciardo, Narain Karthikeyan also drove in the morning session, and could manage a time of just 1:30.722 as he completed 32 laps as the times tumbled in the afternoonÃ¢â‚¬â„¢s dry running.
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BIOGRAPHY: Ethan Hazard
BIOGRAPHY: Daniel Sturridge