Lewis Hamilton was only briefly seen out on track in the rain
Sebastian Vettel had been two tenths of a second in clear in the often-experimental Friday morning session but all three of the front teams were evenly matched.
But Hamilton’s 29 laps in the morning proved to be the majority of the running possible on the first day of practice as a deluge delayed the start of FP2.
Cars were eventually allowed out on track in soaking conditions but few chose to set a lap with the majority instead electing to spend one lap investigating the water on track and then returning to the pits.
The Brit, one of the best drivers in the wet, set the fastest lap of anyone but only the two Williams and two Force India drivers chose to set a time.
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The morning session had been suspended when Carlos Sainz lost control on the exit of Turn 11 to leave his Toro Rosso stricken in the barriers and requiring a crane to get it back to the pits.
But his team where able to perform an impressively speedy repair job to ensure the Spaniard was able to get out during FP2.
However, he was merely performing an installation lap and was one of nine drivers to go out in the rain but not complete an entire lap: Daniel Ricciardo, Romain Grosjean, Pierre Gasly, Kevin Magnussen, Max Verstappen and Valtteri Bottas didn't even do that.
The rain is expected to continue through Friday evening in Japan and could affext Saturday's FP3 session.
But it is expected to stop before qualifying, which could be undertaken in damp, slippery conditions.
And a dry race is expected on Sunday according to local forecasts in Japan.