AUSTIN (AFP) - Defending champion Lewis Hamilton secured his third world title in emphatic and dramatic fashion on Sunday when he raced to victory in a roller-coaster, stop-start, wet-and-dry United States Grand Prix.

The 30-year-old Briton, who started from second on the grid, came home 2.850 seconds clear of his Mercedes team-mate Nico Rosberg to deliver his 10th victory of a dominant season.

Hamilton now has an unbeatable total of 327 points, moving him beyond the reach of both Rosberg, who finished second, and four-time champion Sebastian Vettel of Ferrari, who came home third.

But an emotional Hamilton owed his victory, in the end, to an unforced error by Rosberg on the 49th lap when he made a mistake and ran wide at Turn 15 as the pair duelled for the lead.

That mistake gave Hamilton the lead, victory and his third champions' crown.

"It's the greatest moment of my life," said Hamilton on his car radio, as he seemed to sob and battled his emotions.

"Thank you all so much, I am so grateful to you all. And to my family I love you all. Thank you." Dutch teenager Max Verstappen finished fourth for Toro Rosso ahead of Sergio Perez of Force India, Carlos Sainz in the second Toro Rosso, Jenson Button of McLaren and Pastor Maldonado who was eighth for Lotus.

Felipe Nasr came home ninth for Sauber and Australian Daniel Ricciardo was 10th for Red Bull, having passed two-time champion Fernando Alonso of McLaren on the final lap.

Hamilton's success enabled him to equal the record of Jackie Stewart as the only Britons to win three drivers' world titles and the first to win two championships in succession.

"What a race with all the ups and downs," said Mercedes team chief Toto Wolff.

"It was a fantastic race. We had a problem at the beginning, at the end it was tight, but I'm just overwhelmed.

"Lewis was almost faultless this year and the car didn't let him down. It is just an amazing feeling."