Nico Rosberg believes delaying Mercedes F1 car debut was right decision

The W03 did not appear publicly until last week's four-day Barcelona test, but was reliable enough to complete 399 laps in the hands of Rosberg and his seven-time world champion team-mate Michael Schumacher.

After racking up a further trouble-free 128 laps on the opening day of this week's final test on Thursday, Rosberg said that he was confident of making yet more progress ahead of the Melbourne season-opener later this month.

"I think it shows that bringing the car to the second test [as opposed to the Jerez opener] was the right decision, because we have no reliability problems," he said.

"The reliability is better than last year and it means we can focus more on performance.

"I'm not sure [what it means for Melbourne]. We have to wait and see, but it's great to be part of all this progress."

Rosberg ended the day fifth fastest, completing five back-to-back runs of eight laps each on soft tyres during the morning during which his lap times became more consistent due to a combination of car tweaks and improving track conditions.

He then focused on longer runs during the afternoon with four runs of between 11 and 13 laps on the hard Pirelli rubber.

Afterwards, he said that he was pleased with the level the team is now operating at compared to the same stage last year.

"The tyre degradation is still an issue, but it's certainly better than it used to be; better than 2011. But it's mainly reliability. It's obvious how different that is."

Rosberg hands over to Schumacher for Friday's running before resuming driving duties the following day.