Fernando Alonso edged ahead of Mercedes duo Lewis Hamilton and Nico Rosberg to offer Ferrari a glimmer of hope of success in Canada this weekend.
Despite Mercedes' domination of the current campaign, with the team aiming for a new Formula One record of six consecutive one-twos, it was not the first time Alonso has led the way in practice this year.
Remarkably, double world champion Alonso has now stood at the top of the timesheet on four occasions this year, exactly the same figure as Rosberg.
Naturally, it is only Sunday's results that count, and at present it is Rosberg that leads the way with 122 points, double that of Alonso who lies third in the standings after six races.
Under grey skies over the Circuit Gilles Villeneuve, Alonso clocked a time of one minute 17.238secs, with Hamilton a very close runner-up, just 16 thousandths of a second adrift.
Rosberg had to settle for third quickest on this occasion, 0.146secs down, and as has become the norm, the rest were nowhere.
Four-times champion Sebastian Vettel was down in fourth, just under nine tenths of a second off the pace around the 4.3km track sited on an island in the middle of the St Lawrence Seaway.
As for Alonso's team-mate Kimi Raikkonen, the Finn who has been off the pace so far this season since they became team-mates, he was down in ninth, 1.340secs behind.
Williams' Valtteri Bottas was fifth, followed by Red Bull's Daniel Ricciardo, and then the McLarens.
Despite Jenson Button suggesting the team's cars would not set the track alight this weekend, Button and Kevin Magnussen finished seventh and eighth, separated by three quarters of a second.
Toro Rosso's Jean-Eric Vergne completed the top 10, but 1.4secs back, with Marussia's Max Chilton down in 20th, 3.604secs adrift.
Bringing up the rear was Caterham reserve Alexander Rossi, with the American standing in for Kamui Kobayashi and finishing 4.5secs down on Alonso.