Despite not entertaining the thought of hunting down Lewis Hamilton to launch a fight for the 2015 Formula 1 world title in the final races, Sebastian Vettel admits he is disappointed to be out of the running with three rounds remaining.

Having been pushed onto the back foot coming into United States Grand Prix after Ferrari changed to a fifth engine ahead of the weekend, Vettel nonetheless launched an impressive fight-back from 13th on the grid to get in amongst the leaders on a day of changeable conditions.

Making the most of the conditions to work his way into contention with an alternative strategy, Vettel finished the race on the tail of Nico Rosberg knowing a pass for second would have stopped Hamilton from being crowned champion so early.

Indeed, though Vettel always considered him an outsider in a season that he says has been 'better than anyone expected', he admits to feeling some sadness at falling out of contention.

"Thinking a lot about the season, what we could have done better here and there to squeeze even more out. I think we did a fantastic job, much better than everyone expected, but still it's not great when you lose the fight for the world championship. But, as I said, this is Lewis' day, congrats to him, he deserves to win the championship.

"The race was every exciting - I started 13th, had an average start and then we had a very, very good opening lap and after that we did the right things. Amazing pace when we switched to dry tyres, closing to the field. And then I think it was very close with Nico in the end but not close enough, so that was it."