Nico Rosberg is remaining upbeat ahead of the Australian Grand Prix after positing the second fastest time in free practice at Albert Park, even if he remains distracted by struggles with his brakes and the concerns over fuel saving.

Rosberg, along with Mercedes F1 team-mate Lewis Hamilton, has been touted as the driver to beat coming into the 2014 season opener, the German adding weight to this prediction by joining his counterpart at the top of the end-of-day timesheets.

However, while there is little doubting Mercedes' front-running pace over a single lap heading into the remainder of the weekend, Rosberg remains fairly cautious overall, pointing out that the Hamilton's technical issues in FP1 and fuel consumption considerations mean outright speed is not necessarily enough.

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"I'm optimistic for the weekend, but everything is on the edge," he said. "Reliability, as we saw with my team-mate, isn't something on track and fuel consumption is massively tough, because this is one of the worst tracks for that. Every lap I can see where I should be and I can see what I am doing, and I'm like 'woah', so it is really, really difficult and it's going to be a big challenge for some.

"It's why it's going to be completely different on Saturday and Sunday. Saturday qualifying will be a totally different story to Sunday racing."

Rosberg also signalled his frustration with the new brake-by-wire system, which served to catch out several drivers over the course of the day.

"We've been struggling [with the brakes] too," he added. "It's all settings and you get to an area you haven't been before because you're running the brake balance differently and all of a sudden the rear snaps out because there is some problem we haven't seen yet. It's very delicate because the brake-by-wire is my rear axle, so if I just lock a bit too much I'm off the track."