Melbourne - Nico Rosberg set the pace as Williams upstaged the traditional favourites in both sessions of practice for the opening Formula One race of the season in Melbourne.

The German, third in Melbourne last year, topped the time sheets twice, while team-mate Kazuki Nakajima of Japan was second in the first practice of the day and seventh in the second.

The Williams, along with Brawn GP and Toyota - the three teams subject to protests over the legality of their cars - all did well in the two opening practice sessions for Sunday's race.

Defending world champion Lewis Hamilton in a McLaren-Mercedes was meanwhile 16th in the first outing and only 18th in a field of 20 in the second session around the Albert Park circuit.

Former world champion Kimi Raikkonen of Finland was third for Ferrari in the first session, but 11th in the second session when all the leading teams of last season were off the pace.

Ferrari team-mate Felipe Massa of Brazil was one place better in 10th, but former world champion Fernando Alonso of Spain in a Renault was 12th and the top BMW-Sauber driver was Germany's Nick Heidfeld in 14th.

However Friday's practice is used by teams to test settings and tactics ahead of Saturday's qualification which will determine grid positions for the race.

Rosberg, whose father Keke won the first Australian GP, then in Adelaide in 1985, clocked 1 minute 26.687 seconds in the first session and 1:26.053 in the second, when Brawn GP's Rubens Barrichello - fourth in the first session - was second.

The Brazilian's team-mate Jenson Button was also consistently fast, finishing sixth and fifth. The former Honda team led by owner Ross Brawn is seen as a race favourite after impressive times in pre-season testing.

Toyota also did well with the German Timo Glock eighth and sixth respectively while Italian team-mate Jarno Trulli was third in the second session.

Red Bull's Mark Webber of Australia was fourth in the second session, with team-mate Sebastian Vettel of Germany eighth after technical problems hindered his first run.

Race stewards on Thursday had turned down protests filed by Ferrari, BMW-Sauber, Renault and Red Bull against Brawn GP, Williams and Toyota over their cars.

The teams claim the three teams' diffusers - a part of the car which improves its aerodynamic performance - gives them an unfair advantage.

The teams now intend to appeal the decision to motorsport's ruling body FIA, which would likely not hear the case until after the second race of the season in Malaysia on April 5.