SAO PAULO - Nico Rosberg made the most of a limited supply of tyres on Friday when he topped the times for Mercedes in both free practice sessions for Sunday's Brazilian Grand Prix. The 28-year-old German, who had led a Mercedes one-two ahead of team-mate Lewis Hamilton in the morning, was fastest again, outpacing both Red Bulls in the final minutes of another rain-hit session in the afternoon.

For Rosberg it was confirmation of his merit among the top drivers, many of whom were left frustrated by the lack of available suitable Pirelli tyres in the conditions. "In general, I feel like I had good pace so it can stay wet for the whole weekend for me," he said. "Of course, you don't know where the others were. You would expect the Red Bull to be quicker anyway but I don't know how much fuel they were running. I don't know if pole in the wet is possible as it's too early to say, but I think I've got a good shot at being right at the front in qualifying."

His team-mate and 2008 world champion Briton Lewis Hamilton was not so positive. "If it stays like this I've got no hope," he said. Hamilton added that he was unable to match Rosberg's time because he did not feel as comfortable or competitive in the wet in the Mercedes car as he wished. "Looking back at my career, in the rain... that was when I could really make the difference, but in this car there is no hope for me. I don't know what's going on. I'm just really, really struggling with the throttle mapping and all these kinds of things. Clearly, the car is quick enough because of what Nico was able to do so I really need to work hard," he added.

"I'm just struggling to keep it on the track. It was the same in Australia and I can't remember where else it has been raining, but it has always been the same."

 As a result of the conditions, and the meagre tyre supply, most teams only ran with one set of tyres in order to preserve more tyres for Saturday's practice and the decisive qualifying session for the season-ending contest at Interlagos. While the Mercedes men were split in their reactions to the conditions, world champion German Sebastian Vettel of Red Bull dismissed Friday's action as irrelevant.

"Obviously you can tell that people did not run a lot this afternoon because they wanted to save their tyres, as we only have one set free to use today. But come Sunday, or Saturday, you need to have the tyres -- and you need to make the right call. It was good to get a bit of a baseline in these conditions, but you have to be sharp for tomorrow or Sunday."

Mark Webber, preparing for his last race in Formula One, was third for Red Bull and said he had done his best to prepare for what lies ahead in challenging conditions on a day of virtually incessant rain. Rosberg, who clocked one minute and 24.781 seconds in the morning, was top for most of the afternoon in wetter conditions until it dried sufficiently for the top drivers to risk using intermediate tyres.

This brief late period saw Vettel setting the pace ahead Australian Webber. But Rosberg bounced back to top the times again in 1:27.306, two-tenths of a second faster than Vettel. The champion was second ahead of Webber with Finn Heikki Kovalainen fourth for Lotus, where he has replaced injured compatriot Kimi Raikkonen for the final two events, and Hamilton fifth. Frenchman Jean-Eric Vergne was an impressive sixth for Toro Rosso ahead of local hero Brazilian Felipe Massa, in his last race weekend with Ferrari, German Nico Hulkenberg of Sauber and another Australian Daniel Ricciardo, in his last outing with Toro Rosso before moving to Red Bull next season.