Nico Rosberg says he 'isn't sure what Lewis Hamilton is referring to' following the three-time champion's assertion his Mercedes hasn't been the same since September's Singapore Grand Prix.

In the wake of his second defeat at the hands of Mercedes team-mate Rosberg in Brazil, Hamilton suggested the W06 has behaved differently since Singapore, when the team was unusually out-performed by Ferrari and Red Bull.

"From Singapore onwards there's been a change to the car," he said at Interlagos. "Whether or not that's made a difference, I don't know really. We'll have to see. But it has changed since Singapore."

With Hamilton not expanding on the specific details of his claim, Rosberg says he is uncertain as to why the Briton - who clinched his third title in the United States - is complaining, suggesting the current shift in momentum isn't unusual in their rivalry and shouldn't explained away by other factors.

"I'm not really sure what he is referring to, but there is no change in the feel of the car or anything. For me it was always very close before and now it's just swung the other way.

"It's very close but I'm ahead now and I'm quicker and that's it. Last year I was quicker in qualifying and the beginning of this year I was not and now I am again, so it's just been toing and froing a little bit and at the moment I'm the one with the upper hand."

Though focused on ending the season on a high with a third consecutive victory, Rosberg says his priority is on the race rather than seeing it as an opportunity to take the advantage into the winter.

"The rules are staying the same for next year and whatever is happening this year applies for next year as well, so for sure that's not my priority, it's to win the race, but whatever I can do well this year will help for next year as well. That does come into it, but that's not the main factor. Over the winter, with the new car so much will changes. It's not a complete reset, but it's partial."