Lewis Hamiltion could only manage a disappointing ninth place in the second practice for Interlagos after wet weather hurt the Brit.
In the first practice there was little to separate Hamiliton and fellow title contender Felipe Massa, with the Ferrari driver finishing just 0.190 seconds ahead of the 22-year-old.
However the rain fell for the second practice and whilst Massa coped with the wet conditions, finishing in second behind Fernando Alonso, Hamilition failed to cope with the slippery track.
The McLaren driver must finish in the points should Massa finish either first or second in Sunday's title decider but Hamilton remains in a positive mood ahead of qualifying on Saturday.
"Our car was blindingly quick this morning despite the cold weather, which made the track feel quite slippery," Hamilton told BBC Sport.
"The car felt good. I'm pretty comfortable that we have a good package.
"This afternoon, we focused on our race pace - but we were interrupted by the threat of rain and the changeable wind direction.
"I'm positive that the changes we've made will put us in a good position for tomorrow."
However Massa feels that Ferrari have made dramatic improvements after being outpaced at the Chinese Grand Prix last time out.
"For sure we are more competitive, and when you are more competitive there is more motivation," he said. "It was a good start."
"My aim is to be in front of everyone, both tomorrow and on Sunday. Then we can do the math when it's over."
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