Ferrari's Sebastian Vettel was fastest in final practice at the Canadian Grand Prix as Lewis Hamilton could manage only fifth in his Mercedes.
Vettel was 0.239 seconds clear of Red Bull's Max Verstappen, with Mercedes' Nico Rosberg and Ferrari's Kimi Raikkonen also quicker than Hamilton.
Drivers headed out early to get to work before expected rain, making for a hectic session with many incidents.
The biggest was a heavy crash for Kevin Magnussen's Renault after Turn Eight.
The Dane appeared to make a mistake and lose control under power on a slow lap, possibly because his tyres were not up to temperature.
The incident brought an early end to the session.
Toro Rosso's Daniil Kvyat came close to a crash, too, spinning down the escape road at Turn Four.
Hamilton and Rosberg were among those to miss the fast final chicane after misjudging the entry; Vettel one of several to run wide at the preceding hairpin for the same reason.
This is characteristic of a very difficult circuit, which lacks grip, and features high-speed sections leading into generally slow corners.
Friday's sun was replaced by cooler temperatures and grey skies and the anticipated rain arrived about halfway through, at first spitting, then developing into a very light drizzle.
The track never became particularly wet, but there was enough humidity to render the last 20 minutes or so of the session irrelevant in terms of fast lap times.
Hamilton, who had been fastest in both sessions on Friday, never topped the times and ended the session 0.415secs off the pace and just 0.018secs slower than Rosberg two places ahead of him.
Hamilton is 24 points behind Rosberg in the championship after finally getting his title campaign off the ground following a difficult start to the season with victory in Monaco last time out.
Red Bull's Daniel Ricciardo, who will be a serious contender for pole and victory if it is wet, is a further 16 points adrift.
Ricciardo was sixth, ahead of Toro Rosso's Carlos Sainz and McLaren's Fernando Alonso, who was the only driver in the top 10 to set his fastest time on the theoretically slower super-soft tyre rather than the ultra-soft.
Force India's Sergio Perez and Williams's Felipe Massa completed the top 10, with the second McLaren of Jenson Button 13th.