Nico Rosberg has played down his strong start to the U.S. Grand Prix weekend, saying he is mindful of the threat posed by Lewis Hamilton and Red Bull.
Rosberg topped FP2 in Austin, beating Hamilton by 0.2s in the crucial qualifying simulations. The championship leader has a 33-point lead over Hamilton and would take a big step towards his first title if he won again this weekend.
When it was put to him that he had taken first blood and Hamilton was "struggling", Rosberg laughed and said: "Well, Lewis is certainly not struggling... I wish!
"Today doesn't count for anything, it's just getting to grips with the track. It's been a good day for me with set-up and everything."
He was then asked whether Red Bull would be a threat, to which he said: "Yeah, for sure, just as they have been for the last couple of races and it's no different here at the moment."
Though there is no rain forecast for the rest of the weekend, Rosberg is wary of the impact more subtle weather changes could have on Saturday.
"In general it's been a decent start, I'm feeling OK and the balance is alright out there on one lap as well as the long runs. So good, but early days because tomorrow the wind is going to change 180 degrees, and that changes the car totally and whatever we learn today might not be of any use tomorrow. But that's racing."