Nico Rosberg insists he was not entertaining the thought of allowing Sebastian Vettel to pass him towards the end of the United States Grand Prix, thus preventing team-mate Lewis Hamilton from wrapping up a third world title in Austin.

In a race of high drama, which began with Hamilton and Rosberg clashing at the first corner, the German fought back through to lead into the closing stages only for a mistake with eight laps remaining to allow Hamilton through to win.

Putting Hamilton in position to clinch the 2015 world title with three races remaining, he was nonetheless very nearly made to wait until Mexico as Vettel - the closest driver to him in the standings - mounted a late charge in an attempt to wrest second from Rosberg.

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Indeed, Rosberg's drop in pace in the closing stages raised speculation he was considering allowing Vettel through to spoil Hamilton's success. However, Rosberg - who finished second in the end - maintains he was suffering with tyre degradation

"Of course not. Never. The tyre degradation was pretty bad," Rosberg - who is battling Vettel for the runners-up spot in the standings - told the official F1 website.

Even so, Rosberg remains aggrieved by the outcome of the race, particularly the contact with Hamilton at the beginning, saying he is surprised it wasn't investigated by the stewards.

"Yes, I was [surprised]," he admitted.

"The thing in the first corner was very clear. I was ahead in mid corner and so I have the right to a piece of track - and he is driving me off the road, banging into me. There was a quite heavy contact for me on the steering wheel when we banged wheels - so that was definitely one step too far."

"I have to be cautious with my answer as that could lead to a juicy headline," he continued when asked what he was thinking at the time. "I will keep my first thought to myself."

Rosberg's second place saw him close the gap to Vettel for second in the standings to four points.