Valtteri Bottas led Lewis Hamilton as Mercedes dominated second practice at the Spanish Grand Prix with a performance that will worry Ferrari.
Ferrari have introduced an upgraded engine in Barcelona as the pressure builds to take their first win of the season but lagged behind their rivals.
Charles Leclerc was 0.301 seconds off the pace, with Ferrari team-mate Sebastian Vettel 0.088secs adrift.
Red Bull's Max Verstappen was fifth fastest, 0.751secs slower than Bottas.
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Practice is not always an accurate representation of form in qualifying, and it remains to be seen how the cars will compare when driven to their maximum.
But 0.3secs is about the average advantage Mercedes have had on pace so far this season.
Bottas, who leads the championship by one point after four races, was just 0.049secs quicker than Hamilton, who improved his time on his second lap on the fastest 'soft' tyres while his team-mate did not.
Bottas also headed the first session earlier in the day, when the Finn was 0.115secs quicker than Vettel, with Leclerc a further 0.106secs behind.
And on race pace, Mercedes appear to be even further ahead, judging by the long runs on heavy fuel that the teams do at the end of the session.
The Mercedes cars appeared at least half a second quicker than the Ferraris on equivalent tyres, and on the basis of Friday pace Ferrari look more likely to be fighting off a threat from Red Bull's Max Verstappen on Sunday than they do battling Mercedes for the race win.
Behind the big three, Haas driver Romain Grosjean was best of the rest, ahead of team-mate Kevin Magnussen, McLaren's Carlos Sainz and the Toro Rosso of Daniil Kvyat, who was two places and 0.057secs ahead of Anglo-Thai rookie team-mate Alexander Albon.
British novice Lando Norris was 16th fastest for McLaren and George Russell was the faster Williams driver at the tail of the field, 0.590secs ahead of team-mate Robert Kubica.