* Hamilton takes title with ninth place finish
* Vettel fourth
* Verstappen wins in Mexico (Adds detail, quotes)
By Alan Baldwin
MEXICO CITY, Oct 29 (Reuters) - Lewis Hamilton became Britain's first four-times Formula One world champion at the Mexican Grand Prix on Sunday despite enduring his worst race of the season.
In a race won by Red Bull's Dutch 20-year-old Max Verstappen, the 32-year-old Mercedes driver fought back from last place to ninth after a first lap collision with Ferrari (NYSE:RACE) rival Sebastian Vettel.
Vettel, the only man who could have denied him the championship, started on pole position and finished fourth after having to pit for a new front wing at the end of the first lap and dropping to 19th.
Hamilton now has an unassailable lead of 56 points with two races, worth a total of 50, remaining.
"I did everything that I could. I had a good start. I don't really know what happened at Turn Three - I gave him plenty of room," said a jubilant Hamilton, the British flag draped over his shoulders.
"It doesn't feel real. That's not the kind of race that you want but I never gave up. I kept going right to the end."
Since the start of the season, in which he has won nine times so far, he had not finished lower than seventh.
Hamilton's team mate Valtteri Bottas finished second at the Autodromo Hermanos Rodriguez with Ferrari's Kimi Raikkonen third.
Vettel had needed to be in the top two to have any chance of taking the title fight down to Brazil in two weeks' time but his already slim hopes seemed to have disappeared within seconds of the start.
Verstappen, with nothing to lose and everything to gain from his front row position, seized the lead with an aggressive move through the opening corners and the Red Bull bumping wheels with Vettel as he went through.
Hamilton, starting in third place, tried to follow Verstappen but the Ferrari's front wing hit Hamilton's rear right tyre.
"Did he hit me deliberately?" asked Hamilton over the radio, limping back to the pits with a puncture and fully aware Vettel's only real hope of getting back into the reckoning would be if the Briton went out.
"Not sure, Lewis," his race engineer Peter Bonnington said in reply. Stewards swiftly decided that no further investigation of the incident was necessary.
Vettel pitted while Hamilton, who had started the day 66 points clear of his rival, had a longer stop while mechanics inspected his car for any further damage.
The incident robbed the crowd of the prospect of a real duel between the two contenders, who will both be four-times champions when next season starts, but they still provided thrills as they fought back.
Hamilton had hoped to celebrate the title by spraying the winner's champagne from the top of the podium.
Instead, there was the considerable consolation of being one of only five men -- Germany's Michael Schumacher, Argentina's Juan Manuel Fangio, France's Alain Prost and Vettel -- to win four titles or more since the championship started in 1950.
His tally of titles took him above fellow-Briton Jackie Stewart and also his late Brazilian idol Ayrton Senna in the all-time lists.
"An unusual way to be world champion but you are world champion very simple. Nobody cares how you do it," said Mercedes' non-executive chairman Niki Lauda, himself a triple champion.
The victory was the third of Verstappen's career and second of the season, cementing the youngster's position as the rising star of the sport.