Red Bull's Mark Webber has finished fastest on a wet track in the final practice before qualifying for the Brazilian Grand Prix.
Webber made the most of a brief lull in the rain towards the end of the session to lap the shining, anti-clockwise Interlagos circuit with a best time of one minute 27.891 seconds on Saturday, ahead of Lotus driver Frenchman Romain Grosjean.
The 37-year-old Australian, twice a winner in Brazil, is leaving Formula One after Sunday's race to start a new career with Porsche in endurance racing.
His German team-mate and quadruple champion Sebastian Vettel, who is aiming for a record-equalling ninth win in a row and 13th of the season in Sunday's season-ender, was 17th on a morning when times were meaningless.
Lotus driver Heikki Kovalainen, standing in for the absent Kimi Raikkonen, was third and fellow Finn Valtteri Bottas fourth for Williams.
Most drivers opted to save tyres for later qualifying, with the rain threatening to last well into the afternoon.
"Everybody's sitting in the garage trying to save their extreme tyres because we haven't got that many of them," Red Bull principal Christian Horner told BBC television during the session.
Germany's Nico Rosberg, who was fastest in both Friday practice sessions, did not set a timed lap for Mercedes while British team mate Lewis Hamilton was 11th on team principal Ross Brawn's 59th birthday.
Mercedes' Nico Rosberg, who led both practice sessions on Friday, was among the drivers who did not post a time to try to save tires, along with Fernando Alonso, Jenson Button and Felipe Massa.
Vettel is going into the season-ending race trying to equal Michael Schumacher's 13 victories in a year and match the record of nine consecutive wins by Alberto Ascari.