McLaren pair Lewis Hamilton and Jenson Button said there is more to come from the team after Friday practice for the United States Grand Prix.

Hamilton was the quickest of the pair in fourth place as drivers sampled the Circuit of the Americas for the first time, albeit a second behind pace-setter Sebastian Vettel.

Speaking afterwards, the 2008 title winner - who won the last race in America back in 2007 - was quick to praise the new venue but said McLaren needed to make changes overnight to perform at its best on Saturday.

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"What a great turn-out for a Friday!" he said. "I never expected to see so many people in the grandstands - it makes me feel even more excited for Saturday and Sunday.

"This is a great drivers' track - it's very tough to pull together three perfect sectors. Personally, I find the final two sectors easier than the first; those high-speed changes of direction need a good set-up, and balancing that requirement against the demands of the slow-speed stuff is tricky. Turn One probably looks more exciting from the outside than it does from inside the cockpit - it's certainly not easy, though. You can get oversteer, or lock up, and it's tricky to get a perfect line through there.

"Overall, we've had a good day. Our main difficulty this morning was switching on the tyres in the cooler conditions. But we'll make some changes overnight - there are definitely some improvements we can make."

Team-mate Button, who was a fraction of a second slower than Hamilton in fifth spot, said he has been able to get more of a feeling for the circuit as the day went on in Austin and he admitted the new circuit was one where it could be difficult to pass on race day.

"The circuit was very slippery this morning - as all new track surfaces are, particularly as it was also very cold," he said. "But this afternoon's warmer temperatures meant we could get a better feel for the circuit in FP2.

"Turn One to Turn Nine is a brilliant and free-flowing section - particularly if the car is working well. Turn One is a strange corner though - with a very wide entry rather like Turn Three in India. Turn Three here - the start of the esses - is fantastic though. It's quicker than Becketts at Silverstone. It's very unusual to find a section of corners like this on a modern Formula 1 track. I love it.

"Nevertheless, I don't think overtaking is going to be easy here, because it'll be so tricky to stay close to the car in front of you. But the circuit is great fun to drive, and I hope we can put on a great race."