Brazilian GP: Nico Rosberg completes clean sweep in practice

In dry, overcast conditions the German recorded a time just 0.114 seconds faster than his Mercedes team-mate Lewis Hamilton, having also topped both Friday sessions.

The Williams drivers were again best of the rest behind the Mercedes as Felipe Massa and Valtteri Bottas set the third and fourth quickest times.

But all the teams were anxiously looking at the weather radars as rain is forecast for the afternoon's qualifying hour.

Hamilton's session wasn't without incident, as he locked up and spun under braking for the Senna S early on.

Then at the end of the hour he was baulked by a Lotus in the twisty part of the lap while on a quick run.

Local hero Massa was one of the main pacesetters throughout the session as he and Williams team-mate Bottas traded fastest laptimes, but it was when the Mercedes switched to the softer tyres that they resumed their customary place at the top of the timesheets.

Red Bull's Daniel Ricciardo was fifth quickest ahead of the McLaren of Jenson Button.

They finished in front of the two Ferraris of Fernando Alonso and Kimi Raikkonen.

Dane Kevin Magnussen took ninth overall ahead of Daniil Kvyat who rounded out the top 10.

Sergio Perez was the slowest of the 18 runners, putting in 25 laps following his lack of running on Friday.

He goes into qualifying with a seven-place grid penalty following his first-lap contact with Adrian Sutil at Austin.