Marc Marquez surprised even himself as he concluded the first day of free practice at the Circuit of the Americas in Austin a second clear of his nearest rival.

The reigning MotoGP world champion claimed his debut premier class victory at the Circuit of The Americas last season and began his preparations for the weekend in ominous fashion, taking the top spot by 1.005s from Ducati's Andrea Dovizioso with a best lap of 2m 03.490s.

Marquez, who opened the defence of his crown in perfect style with victory over Valentino Rossi in the night race in Qatar in March, said: "It's a great surprise because you never expect to be so fast by plus one second; you expect to fight for the pole position but you never expect to have that advantage.

"But I feel good and already we have a good base with the set-up and we are quite encouraged. I think tomorrow the other ones will improve - we are only on Friday."

Asked why he is particularly strong at the spectacular Texas track, Marquez added: "I don't know - we are happy with this track. It's one of my favourite tracks and I like it."

The young Spaniard managed to succeed in Qatar despite barely recovering from a broken leg suffered in a dirt bike training accident and admitted he was still affected slightly by the injury, although he completed FP1 and FP2 without pain killing injections.

"For rhythm a little bit [the injury is troublesome], especially in T1 and T2 where there are many changes of direction," he said. "I was struggling a little bit but I think everybody is struggling. Today I ride without painkillers and it was great, tomorrow we will see if it is better.

"When I feel ok with my leg then I will ride [dirt bikes] again. If I do not feel 100 per cent then I will not ride dirt tracks."

Marquez said he feels greater pressure to win in Austin, but nonetheless is treating round two of the championship as 'just another race'.

"Yes of course [I feel pressure to win]. I don't know why this race is more pressure to win but it looks like if I don't win on Sunday it will be a disaster!" he said.

"In the end it's another race and we will try to win of course - that is my goal but if we cannot win we will try to stay on the podium."

Ducati rider Dovizioso's lap was set on the special soft rear tyre only available to Ducati and the Open class, meaning Marquez's like-for-like advantage was 1.133s over team-mate Dani Pedrosa who, like Marquez, also used the hard rear tyre in the afternoon.