Mercedes suggested they could be the team to beat at the Canadian Grand Prix as Lewis Hamilton and Valtteri Bottas ended first free practice well clear of Ferrari. Hamilton led Bottas by a couple of tenths, but third-fastest Charles Leclerc was a second adrift in the leading Ferrari.
Mercedes' joy was tempered slightly as Bottas' session was ended a few minutes early by a fuel-pressure problem.
To give the red cars a further headache, Max Verstappen split them in fourth place as Red Bull look to prove that they can mix it at power-hungry tracks with Honda on-board in 2019.
Kimi Raikkonen ran best of the rest for Alfa Romeo, suggesting that there is significant speed coming from the Ferrari power unit, although his team-mate Antonio Giovinazzi lost time after hitting the barriers coming out of Turn 9 and damaging the rear left of his car.