Lewis Hamilton topped the times ahead of team mate Valtteri Bottas as Mercedes, using a new power unit, dominated Friday's opening free practice session for this weekend's Canadian Grand Prix.
The defending five-time world champion clocked a best lap in 1min12.767sec to outpace Bottas by 0.147sec, the pair leaving third-placed Charles Leclerc of Ferrari adrift by nine-tenths.
Max Verstappen was fourth for Red Bull ahead of four-time champion Sebastian Vettel of Ferrari and Kimi Raikkonen of Sauber.
Bottas's session ended slightly early when he reported some misfiring with his new engine with five minutes remaining. The team identified that his car had "lost fuel pressure" and he was required to retreat to the garage.
Carlos Sainz was seventh for McLaren ahead of Daniel Ricciardo of Renault, Sergio Perez for the Canadian-owned Racing Point team and Kevin Magnussen of Haas.
Hamilton, who leads Bottas by 17 points after a record six successive season-opening Mercedes victories in 2019, is hunting a record-equalling seventh victory in Canada and a record seventh pole position.
At one stage after half an hour, the two Mercedes men clocked identical laps in one minute and 13.495 seconds, a statistical rarity in a sport measured in milliseconds.
The pair traded fastest laps through most of the session run in dry and warm conditions at the Circuit Gilles Villeneuve.
After an hour, Italian rookie Antonio Giovinazzi was the first man to smack into the wall at Turn Nine, in his Alfa Romeo, prompting a Virtual Safety Car (VSC).
He was unhurt, but his car had a damaged left rear wheel.