Suzuka: Mercedes pair Lewis Hamilton and Nico Rosberg showed flashes of pace in Friday`s second free practice in Japan before heavy rain effectively washed out much of the afternoon session.
Red Bull`s Daniil Kvyat topped the timesheets at a soaking Suzuka, clocking one minute, 48.277 seconds with Rosberg 0.023 back and reigning world champion Hamilton a further half-a-second slower.
Rain had created havoc in the morning practice, when only 12 drivers completed a timed lap as they struggled to keep control of their aqua-planing cars.
Mercedes, looking to fix a mysterious loss of pace in Singapore last weekend, shot out to the quickest times in the second session, before Kvyat backed up an impressive early display by edging ahead of Rosberg.
But just as things began hotting up, the rain returned to send the cars back to their garages and when Hamilton finally emerged on wet tyres, he was warned over the radio "be mindful of the rivers," so soggy were the conditions.
Daniel Ricciardo clocked the fourth fastest time behind Hamilton with Singapore winner Sebastian Vettel steering his Ferrari to the fifth-quickest time.
Vettel put in a shift despite the atrocious weather, completing 19 laps, correcting a heart-stopping slide through the quick right-hander between the hairpin and Spoon as he ran fourth in the morning.
Rosberg also survived a couple of early scares in a hair-raising first practice, braking late into the chicane and sliding onto the run-off.
Toro Rosso`s Carlos Sainz was quickest in the first session in a time of 1:49.434, half-a-second clear of Kvyat, but the Spaniard struggled in the afternoon, complaining of "strange noises" coming from his engine.
With memories of Frenchman Jules Bianchi`s fatal crash at a wet Suzuka last year certain to make Sunday`s race an emotional one, drivers were anxious to avoid taking any risks in the treacherous conditions.
Hamilton, who suffered his first retirement in over a year last week, will be frustrated Friday turned into little more than an exercise in data analysis but the Briton still leads the championship by 41 points with six races left.
Jenson Button, whose Formula One future is in doubt after talks over a contract extension with McLaren appeared to have stalled, complained of "massive understeer" and finished 12th, over three-and-a-half seconds adrift.
Meanwhile, Fernando Alonso went out after McLaren switched his engine, Honda having discovered a problem after the morning practice.
The double world champion cut a forlorn figure staring out into the gloom for the first 40 minutes, and eventually finished 17th.