'Hamilton and Rosberg feeling the pressure'

Formula One title rivals Lewis Hamilton and Nico Rosberg are under huge pressure as they enter the final straight, however much they try to hide it, Mercedes team boss Toto Wolff said on Friday.

"I think that generally, all of us, we underestimate the pressure that is on these guys," Wolff told reporters at the U.S. Grand Prix.

"It's a couple of races towards the end of the season, there is all to win and all to lose," added the Austrian in response to a question about triple world champion Hamilton's behaviour towards the media in Japan two weeks ago.

Hamilton drew criticism at Suzuka for fiddling around with his mobile phone during a news conference and using the Snapchat app to alter pictures of fellow drivers. He also walked out of a later media briefing.

That race in Japan came only days after he had retired with an engine failure in the closing stages of the Malaysian Grand Prix while leading the race.

Hamilton is now 33 points behind Germany's Rosberg with four races remaining, meaning that even if the Briton takes four successive victories it may not be enough to win the title.

"I guess that after Malaysia, where he (Hamilton) was in the lead, 25 points to take, the engine blew up. That was a very difficult situation for him to cope with," said Wolff.

"As cool as someone might seem to be outside, inside it kind of eats you up and maybe that’s why the weekend in Suzuka was a bit difficult for him emotionally.

"But he knows exactly that there’s a job to be done in the car and there’s a job to be done outside the car."

Hamilton's demeanour in Austin has been radically different, to the point where the words 'charm offensive' were on many reporters' lips after he again appeared in the official Thursday news conference.

He appeared controlled, courteous and answered all the questions addressed to him.

Rosberg has also been impressively calm, insisting that he is not thinking about the title but taking each race in isolation.

Wolff, who flew back from Japan to Britain with Hamilton where they attended celebrations at the factories to celebrate the team's third successive constructors' title, said there had been conversations with the driver about what had happened.

"It was generally about how things can be improved. It was not a headmaster kind of discussion," said the Austrian.