By Alan Baldwin
SUZUKA, Japan (Reuters) - A rain soaked first Japanese Grand Prix practice on Friday provided no immediate answers to questions about how Formula One world champions Mercedes would fare after their mysterious Singapore slump last weekend.
Championship leader Lewis Hamilton was fifth fastest for Mercedes but the Briton spent most of the time in the garage and completed only six laps, while title rival team mate Nico Rosberg was third.
Eight of the 20 drivers failed to set a time on a slippery track with steady rain and cars throwing up plumes of spray when they did go out.
Spanish rookie Carlos Sainz was fastest for Toro Rosso, despite problems with aquaplaning, with a best time of one minute 49.434 seconds.
It was the first time in his 14 race career that Sainz had led a session.
Red Bull's Russian Daniil Kvyat was next on the time sheets but half a second slower while Hamilton's best lap was 1.288 seconds off the pace but meaningless given the conditions.
Ferrari's Sebastian Vettel, winner from pole position in Singapore for his third victory of the season, was fourth quickest but on intermediate tyres rather than the full wets used by Hamilton.
Brazilian Felipe Massa, in a Williams, and Ferrari's Kimi Raikkonen both had spins.
Vettel's speed in Singapore raised questions about whether Mercedes were suffering circuit-specific problems or whether Ferrari and Red Bull had managed to rein in their hitherto dominant rival.
Suzuka, a fast track with challenging corners, should be much more to Mercedes' liking but both Hamilton and Rosberg had hoped for more reassurance than they were able to get from Friday's session.
Financially-struggling Lotus, whose freight was delivered only on Thursday, remained locked out of their paddock hospitality due to payment problems.
Lotus reserve driver Jolyon Palmer, replacing Romain Grosjean for the session, managed only an installation lap and later Tweeted a picture of himself 'enjoying' the team's VIP hospitality -- sitting on the floor of the garage with a packet of crisps.
(Reporting by Alan Baldwin; editing by Julian Linden)