By Tatiana Ramil
SAO PAULO (Reuters) - Nico Rosberg hoped for a rainy weekend after splashing through spray and standing water on Friday to put Mercedes on top of both practice sessions for the season-ending Brazilian Grand Prix at Interlagos.
Limbering up for what could be a battle of the Germans on Sunday, Rosberg kept Red Bull's quadruple world champion Sebastian Vettel in second place on the timesheets.
Rosberg was quickest in the morning with a time of one minute 24.781 seconds, set early on before conditions became trickier, and again fastest in the afternoon with a lap of 1:27.306.
Vettel, chasing his ninth win in a row and 13th of the season, was 0.225 of a second slower in the afternoon.
"It felt good and it was a good day in the wet," said Rosberg. "It looked like a good pace so for me it can stay wet this weekend...I think I've got a good shot at being right at the front in qualifying."
More rain is expected on Saturday for final practice and qualifying although conditions at Interlagos can change suddenly.
Rosberg's team mate Lewis Hamilton had been second quickest before lunch but, unusually for a driver who excels in the wet, struggled in the afternoon at a circuit where he won his world title in 2008.
"Looking back at my career, in the rain was when I could really make the difference but in this car there is no hope for me," said the Briton gloomily.
Vettel and Australian team mate Mark Webber completed the top three in the second session.
The German can equal compatriot Michael Schumacher's 2004 record of 13 wins in a season as well as Italian Alberto Ascari's 60-year-old record of nine victories in a row if he triumphs on Sunday.
Vettel already holds the record for eight successive wins in a single season.
Webber, preparing for his final Formula One race with both world titles already won by his team and Vettel, suffered another of the KERS failures that have plagued his recent career and was also keeping plenty of tyres in reserve.
"Not many people went out this afternoon in order to save tyres for the weekend," said Vettel.
"It's a bit of a shame for those in the grandstands but unfortunately it's like this. Come Saturday and Sunday we may need to have the tyres available."
Finland's Heikki Kovalainen, filling in at Lotus for compatriot Kimi Raikkonen, was fourth fastest in the afternoon ahead of Hamilton.
The times were largely meaningless with the weather triggering plenty of slides, spins and off-track excursions.
Vettel was alone in trying out Pirelli's slick 2014 development tyre in the morning, completing a cautious lap with sensors on the car before being told by his race engineer that they had all the data they needed.
With the championships wrapped up last month, the main focus for his rivals this weekend is the battle for second place between Mercedes, Ferrari and Lotus as well as various farewells.
Mercedes are 15 points ahead of Ferrari with Lotus a further 18 behind.
McLaren's Jenson Button - last year's winner at the Sao Paulo circuit - was fourth quickest in the morning but last in the second practice ahead of a weekend that could see his team's season confirmed as their worst in decades.
If 2009 world champion Button or Mexican Sergio Perez fail to finish in the top three on Sunday, it will be the first time since 1980 that McLaren have gone a whole season without a podium appearance.
Ferrari's Fernando Alonso was fifth and 11th while Brazilian team mate Felipe Massa was 11th and seventh for his last race in the Italian team's colours before moving to Williams.
"It's hard to establish how the weekend will go because even if we weren't quick today in the rain it's too early to say what conditions will best suit our car," said Massa whose last race win was in Brazil in 2008. (Writing by Alan Baldwin in London, editing by Justin Palmer)