Lewis Hamilton led Valtteri Bottas as Mercedes dominated first practice at the Canadian Grand Prix.
Hamilton was 0.147 seconds ahead of his team-mate, Ferrari's Charles Leclerc in third was a huge 0.953 seconds behind.
Leclerc's team-mate Sebastian Vettel had a spin at the hairpin on his way to fifth fastest, 1.138secs off the pace.
Red Bull's Max Verstappen split the Ferraris, while Alfa Romeo's Antonio Giovinazzi crashed as drivers battled with a dusty and slippery track.
A number of drivers had 'moments' through the session on a track that is little-used through the season and runs through what is normally a public park on the picturesque Ile Notre Dame in the St Lawrence Seaway beside the city of Montreal.
Haas driver Romain Grosjean was another to spin, while Red Bull's Pierre Gasly and Toro Rosso's Daniil Kvyat had off-track moments.
Bottas' session ended a few minutes early when he was pulled into the pits with a lack of fuel pressure, a rare show of vulnerability in this season in which Mercedes have so far swept all before them.
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The silver cars have won all six races so far, Hamilton taking four victories and Bottas two and the Briton is leading the Finn by 17 points in the championship, with Vettel 45 points behind.
On the face of it, Mercedes again look strong favourites for the weekend, despite this being a track that should suit the Ferraris, which have been quick on tracks with similar characteristics of long straights and slow corners this season.
Mercedes have introduced an upgraded "phase two" engine into their factory and customer cars this weekend. Ferrari have fitted new turbochargers and MGU-Hs to the cars of Leclerc and Vettel. The MGU-H is the part of the hybrid system that recovers energy from the turbo.
Alfa Romeo's Kimi Raikkonen was sixth quickest, with McLaren's Carlos Sainz, Renault's Daniel Ricciardo, Racing Point's Sergio Perez and Haas' Kevin Magnussen completing the top 10.