Sebastian Vettel has played down his dominance in practice ahead of the United States Grand Prix, but he was not fooling Fernando Alonso.

The two title rivals finished first and third at the end of the two 90-minute sessions as the Circuit of The Americas played host to Formula One for the first time.

Such a scenario in Sunday's race would ensure the title fight between the duo would go down to the wire in Brazil as Vettel needs to finish 15 points clear of Alonso to secure a third successive title.

At the end of the first session on a very slippery track, Vettel was 1.4 seconds ahead of McLaren's Lewis Hamilton, the largest margin at the end of any practice run this season.

That was halved in FP2, although Vettel was hampered by a water leak from his Red Bull.

When he did emerge again he immediately went quicker and was never headed, finishing three quarters of a second faster than team-mate Mark Webber and Alonso in his Ferrari.

Despite that, Vettel said: "On a Friday you need to be careful, also the fact that it's very slippery can make a big difference, a bigger difference than you think.

"There were no surprises for us." - Alonso

"I think there were more than one or two surprises in terms of pace and people, so we'll see what happens as the track will constantly improve, and we'll go from there."

Alonso, trailing Vettel by 10 points going into the final two races, knew better than to believe the 25-year-old German.

"There were no surprises for us," said Alonso.