Listen to final practice and qualifying on 5 Live Sports Extra, Saturday from 02:55 GMT
Lewis Hamilton headed a Mercedes one-two in second practice at the season-opening Australian Grand Prix.
Hamilton beat Valtteri Bottas by 0.048 seconds but the two were 0.8secs clear of the two Red Bulls of Max Verstappen and Pierre Gasly.
Ferrari, who appeared to have the quickest car in pre-season testing, were fourth with Sebastian Vettel.
The suspicion is that the Italian team were hiding their true pace ahead of qualifying on Saturday afternoon.
Can football tell us if Ferrari are faster than Mercedes?
Vettel was 0.8secs slower than the Mercedes on both short, qualifying-style runs and longer race-style runs, which is completely contradictory to their form in testing, when all their rivals felt Ferrari were ahead.
Ferrari playing games?
The session left plenty of intrigue ahead of qualifying on Saturday, when the cars' true pace will be shown for the first time.
Vettel ended the day 0.873secs slower than Hamilton, a result that, if it were repeated on Saturday afternoon would surprise the whole paddock.
The German was just 0.03secs slower than Hamilton in the first session of the day, but while Mercedes found a second for the next session, Vettel improved only by a couple of tenths.
Adding to the confusion, on the race-distance runs late in second practice, Vettel on the fastest 'soft' tyre was no faster than team-mate Charles Leclerc on the slowest 'hard'.
Alfa Romeo's Kimi Raikkonen was fifth quickest - just 0.099secs behind his former Ferrari team-mate Vettel.
That margin added to the suspicion that Ferrari might have been playing games because the margin between Vettel and Raikkonen was smaller than it was on average between them when they were team-mates. So for Raikkonen to be that close in a car that will undoubtedly be slower only emphasised the point that Ferrari can find plenty more time.
Renault's Nico Hulkenberg and Daniel Ricciardo were seventh and eighth, closely matched after the Australian had a tricky day with a number of delays, first due to a technical problem and then the need to adjust his seat to reduce discomfort in the car.
Leclerc was only ninth fastest, ahead of the Haas of Romain Grosjean.
British novice Lando Norris was 18th fastest in his McLaren, 0.6secs and four places behind team-mate Carlos Sainz.
For Williams, it looks like being a long season. British rookie George Russell and team-mate Robert Kubica, returning after eight years away following the rally crash that left him with life-changing injuries, were 19th and 20th.
Russell was 0.2secs ahead of the Pole - but they were nearly two seconds slower than Norris.
A Scuderia beard - maybe one for Vettel to try later in the seasonBright sunshine welcomed fans at Albert Park for first and second practiceRicciardo showed off his new helmet with its dazzling pink, green and blue design
