Lewis Hamilton topped the times ahead of Mercedes team-mate George Russell in Friday's delayed and rain-curtailed practice for this weekend's Canadian Grand Prix.
The two 'Silver Arrows' snatched a rare opportunity to claim the initiative with laps on soft tyres shortly before heavy rain finally arrived at the Circuit Gilles Villeneuve with five minutes remaining of the extended second session.
The earlier opening session had been reduced to only five minutes' action following a technical failure.
Hamilton topped the times with a best lap in one minute and 13.718 to outpace Russell by 0.027 seconds ahead of Ferrari's Carlos Sainz and two-time champion Fernando Alonso of Aston Martin.
Charles Leclerc was fifth in the second Ferrari ahead of defending double world champion Max Verstappen of Red Bull and Valtteri Bottas in his Alfa Romeo.
Sergio Perez was eighth in the second Red Bull ahead of local hero Lance Stroll in the second Aston Martin and Pierre Gasly of Alpine, whose driveshaft failure in opening session caused the red flag that ended that session.
Overall, it was an intriguing day of unexpected action that began in warm sunshine and ended in heavy rain with the revamped Mercedes team back on top.
After the earlier non-event of FP1, when only 12 cars led by Valtteri Bottas's Alfa Romeo, clocked times in a session reduced to five minutes, the extended session began in warm and cloudy conditions.
The air temperature was 23 degrees Celsius and the track was measured at 39 at the fast semi-street track, built on the Ile Notre Dame in the St Lawrence Seaway, as Bottas led the way again.
The organisers had pronounced that the technical failures which led to "issues with the local CCTV system" had been resolved, much to the relief of a big and frustrated Friday crowd.
Bottas was first to clock a time before Leclerc went top before Alonso and Bottas again took the initiative on the low-grip circuit, lined with barriers and kerbs and demanding for brakes.
Verstappen rose to the top after 10 minutes ahead of Sainz as the drivers became accustomed to the green track and evaluated their many upgraded parts.
As the action unfolded, Gasly, Sainz, Verstappen and Leclerc enjoyed top spot before two red flags interrupted the progress – Nico Hulkenberg pulling up in his Haas with smoke billowing from his engine and then Esteban Ocon pulled up in his Alpine at the chicane with a suspected driveshaft failure.
Following the second interruption, both Mercedes went out on softs and clocked quickest laps, Russell doing so first before Hamilton went top as heavy rain clouds approached.
The rain did not arrive immediately, but Red Bull sent both drivers out on intermediates for a lap, on a dry track, with a wind gusting. Mercedes followed suit and, with six minutes remaining, the rain arrived.
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