US GP: Mercedes' Nico Rosberg says he has time in his pocket

The Mercedes drivers were separated by only three thousandths of a second on their best laps of the day, and Rosberg is confident he can find more time as the weekend rolls on.

"It's tight as usual - three thousandths - but I have them in my pocket," Rosberg told reporters in the Austin paddock after Friday's running.

"I know where they are, so no worries. I'm going to pull them out tomorrow.

"It's been a good day for us; the car is really quick here, again."

Rosberg had a brief moment of concern during FP2 when he accidentally knocked his clutch paddle, and he explained that it was due to an itch on his foot.

"I lifted my leg and hit my clutch pedal, because I got an itch," he said.

"Can you imagine of all the things that can happen! So that turned into a bit of an issue.

"I need to make sure I don't lift my foot when I get an itch..."

HAMILTON PLAYS DOWN LEAK

Hamilton's running was cut short on Friday afternoon when his car developed a leak, but the championship leader said it was not a major cause for concern.

"They just said 'you've got to stop, there's something wrong with the car' - I don't think it particularly affects the weekend," he said.

"They pulled the floor off and there was some kind of fluid, some kind of leak.

"I had to stop just in case. The gearbox was working fine, the race 'box goes in tomorrow I'm confident it will be fine."

Rosberg added that it was a concern for the team to still be battling reliability gremlins as the season draws to a close.

"Of course it's worrying to see his car broke down," said the German.

"We need to see what it is and get on top of it and hopefully it doesn't impact the race weekend.

"I have full confidence in the team, but of course it's not ideal. It shows our car is still not 100 per cent robust."