On a day when Renault-powered cars completed just 19 laps in total - and when reigning champion Sebastian Vettel managed just eight in Red Bull's new RB10 - Rosberg clocked up 97 laps, including two double-digit stints.
While he insisted his focus was not on his likely 2014 rivals, Rosberg said his marathon day had been a massive boost for the team - particularly given Lewis Hamilton's front wing failure on the first day.
Jerez test day two report
"For sure I'm smiling, the team did a great job," he said.
"Yesterday went a bit wrong with Lewis having a shunt but they fixed the bits during the night and flew them out, so thanks to all of you in England for fixing that.
"We had such a great day - we just drove and drove, loads of laps and that's what we need at the moment.
Mercedes W05 technical analysis
"That's how you can really progress and get rid of the reliability problems and understand everything better, so it's been a very positive day.
"I don't know about comparing to other people - it is just one day that went well for us. Yesterday went poorly for us, so you need to be careful.
"But I can look at ourselves and say we're on target today, with the amount of kilometres we were able to do."
Jerez test gallery
Rosberg emphasised that with plenty more upgrades to come before Melbourne, the focus remained on mileage rather than set-up or development work
"At the moment the cars are still quite far off [Melbourne spec].
"I'm sure there will still be performance to come.
"At the moment it's about getting kilometres, [solving] reliability problems and trying to get to the finish line in the first couple of races while at the same time trying to improve our actual speed.
"With a day like today we're on track."
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