"I can assure you that Michael was still on it," Rosberg insisted.
Whatever the case, the German's skills will be tested yet again in 2013, now that Lewis Hamilton - undisputedly one of the very fastest in F1 - is his teammate.
Years ago, the pair were teammates in the upper classes of go-karting.
"He (Hamilton) was super-fast," Rosberg admitted.
He thinks, however, that he might have the upper hand now that they share identical formula one cars.
"Karting is pure, but in formula one, my other strengths come into play much more," said Rosberg.
"I always get the most from the setup; I am very consistent," he said, raising the idea that Hamilton is more of an instinctive driver.
"There are drivers who have days where not everything fits together. I have less of them," added Rosberg.