The Brawn GP driver won the F1 title after finishing fifth in the Brazilian Grand Prix. Celebrations for Button mean disappointment for the German Sebastian Vettel, however, who now sits in second with one race to go.
"We are the champions," Button sang – albeit out of key – from his cockpit after crossing the finishing line and capturing the title with one race left in the season.
"It's really amazing especially after the last few weeks. It was such an awesome race. When I first jumped in a car 21 years ago I never expected to be world champion - but we did it today," the 29-year-old Brit told reporters after the race.
After Button's opening win at the Australian Grand Prix, his wire-to-wire triumph turned into a case of the tortoise and the hare in the second half of the season, as he survived the intensifying pressure around him.
But he continued to collect points and took the title with a solid drive in Sunday's dramatic 71-lap race.
Disappointment for Vettel
Sunday saw German Sebastian Vettel's hopes of glory vanish. The young gun Red Bull driver came in fourth ahead of Button, giving him a season total of 74 points and placing him in second place in the standings for the time being.
In the end, heavy traffic and a late puncture kept the German out of contention, with Australian Red Bull driver Mark Webber taking the Brazilian title. Polish BMW driver Robert Kubica took second in the race, while the British Mercedes driver Lewis Hamilton came in third.
Swiss Sebastien Buemi of Toro Rosso was seventh and the local hero, Brazilian veteran Rubens Barrichello, eighth after starting from pole position.
glb/AFP/Reuters/dpa
Editor: Ranty Islam
Red Bull driver Mark Webber won the FIA Formula One 2009 Grande Prêmio Petrobras do Brasil Saturday at Autódromo José Carlos Pace, São Paulo, Brazil. 

Interlagos (Autódromo José Carlos Pace)
Robert Kubica came in second for BMW Sauber, and Lewis Hamilton finished third for McLaren.

Webber's teammate Sebastian Vettel started from 15th place on the starting grid after he couldn't come up from the first qualification session, but finished 4th in front of his championship rival.

Brawn Grand Prix driver Jenson Button finished 5th to win his title. His team, representing the remnants of Honda Racing, also won the 2009 Constructors' championship after leading through the season.

The team's road to victory was not smooth — a scandal broke with the "double-decker diffuser" of the BGP001 car.  After the FIA declared them legal and other teams started to borrow the idea, Brawn sped up by collecting points on the way to the title.

Brawn GP, the winning constructor
Kimi Räikkönen (Ferrari) and Sébastien Buemi (Toro Rosso) dropped one place from the starting grid and finished behind Button.

Button's teammate and possible vice-champion Rubens Barrichello, who won pole position on his home soil after nearly three hours of a long rainy qualification session, had a tire puncture on the dying laps of the race and was forced to make an unscheduled third visit to his pit. He closed in the top eight.

This Brazil GP featured Japanese rookie driver, Kamui Kobayashi (Toyota), who replaced recovering Glock. In his first race this young driver qualified 11th and finished 10th in the race.

Adrian Sutil qualified 3rd for Force India, but was taken out by Jarno Trulli (Toyota) on the first lap.