Mercedes lead the way in Spanish Grand Prix practice in Barcelona
Mercedes, with Valtteri Bottas again quicker than reigning world champion Lewis Hamilton, led the way in first Spanish Grand Prix practice on Friday with Ferrari's Sebastian Vettel the best of the rest.
Bottas put down a marker with a best lap of one minute 18.148 seconds on the soft tyre, 0.849 faster than his four-times champion team mate who won from pole last year.
Vettel, who will be chasing his fourth successive pole position on Saturday, was on the quicker supersofts but 0.950 slower than the Finn around a sunny but windy Circuit de Catalunya.
Hamilton leads the German, also a four-times world champion, by four points after four races.
Red Bull's Max Verstappen was fourth fastest but Australian team mate Daniel Ricciardo crashed in his first track session since the two drivers collided in the Azerbaijan Grand Prix 12 days ago.
The virtual safety car was deployed briefly, with Ricciardo's car running across the gravel and into the barriers, with several others also spinning. The Australian was classified seventh.
Home hero Fernando Alonso started the weekend a morale-boosting sixth, behind Ferrari's Kimi Raikkonen, with his McLaren displaying a heavily-revised three-pronged nose.
Williams had another trying session as Polish reserve Robert Kubica took part in a race weekend for the first time since 2010, three months before he suffered serious injuries in a rally crash.
The former race winner was 19th, in 1:21.510, but faster than teenage Canadian team mate Lance Stroll in last place on the timesheets with a best of 1:22.756 after an off into the gravel.
"Unbelievable how bad the balance is," Stroll complained over the radio.
Kubica was replacing Russian rookie Sergey Sirotkin, who returns for second practice and the race but has a three-place grid penalty.