Lewis Hamilton trails Nico Rosberg in Australia practice
Nico Rosberg narrowly beat team-mate Lewis Hamilton to fastest time as Mercedes dominated the first practice session of the new season.
Rosberg was just 0.029 seconds quicker than the champion as Mercedes were more than a second clear of the field.
Williams's Valtteri Bottas was third ahead of Toro Rosso rookie Carlos Sainz and Ferrari's Sebastian Vettel.
Neither Sauber, locked in a legal dispute with ex-reserve driver Giedo Van Der Garde, nor Manor did any laps.
Van Der Garde is claiming he has a contract to race for the Swiss team, who have signed Swede Marcus Ericsson and Brazilian Felipe Nasr as well, and has taken the case to the Australian courts, who have ruled in his favour.
But the Dutchman cannot drive the Sauber as he does not have a valid F1 licence.
Sauber are believed not to have run because the case is still ongoing on Friday in Melbourne and they risk being in contempt of court.
|Chief F1 writer Andrew Benson on the Australian GP|
|"It's hard to think of a better place to start the season than Melbourne and somehow it would not seem right if the opener was anywhere else.|
|It's an awfully long way to go for a motor race but the reward is a vibrant, fun city, a view of Port Philip Bay, and one of the loveliest venues on the calendar.|
|The autumn leaves are just starting to fall in Albert Park when Formula 1 pops by, the air is scented by pine and eucalyptus and the atmosphere crackles with anticipation of the season ahead. And the track, a mix of street and road circuit, with walls ever close, pretty much guarantees action of one kind or another."|
Manor, who only just made it to Australia after a late rescue from financial problems that forced them to miss the final three races of last season, had problems with their engine software.
The Mercedes advantage over the field - 1.191 seconds - was in the region of what was expected after pre-season testing.
Williams, Ferrari and Red Bull were expected to be engaged in a tight battle to be best of the rest, but Bottas had an advantage of nearly 0.3secs over Vettel, who was just ahead of the second Toro Rosso of Max Verstappen, who at 17 is the youngest driver in F1 history by nearly two years.
Williams's Felipe Massa was seventh ahead of Ferrari's Kimi Raikkonen, Lotus's Pastor Maldonado and the Red Bull of Daniel Ricciardo, who had a spin at Turn 15 after putting a rear wheel on the grass on the approach.
McLaren-Honda's troubles continued. Jenson Button managed just six laps and team-mate Kevin Magnussen seven - achieving 14th and 15th fastest times - before the team ran into yet another problem with the Honda engine.