Nicky Hayden snatched the MotoGP crown from the grasp of five-time champion Valentino Rossi following a dramatic final race in Valencia on Sunday.
Hayden was overwhelmed after beating the odds
Rossi led the standings by eight points before the race but saw his hopes end after sliding out on lap five.
He got back on his Yamaha and finished 13th but American Hayden, 25, came home in third to take the title for Honda.
Australia's World Superbike champion Troy Bayliss, riding in place of the injured Sete Gibernau, won for Ducati.
Hayden's title chances looked over just a fortnight ago when he crashed out of the Portuguese MotoGP after being hit by team-mate Dani Pedrosa.
You dream about being world champion and dedicate your whole life to it, so when it comes true it is very special
But the 'Kentucky Kid' bounced back to become the first American to win the premier class title since Kenny Roberts Jr in 2000.
"I'm just real, really proud," said an emotional Hayden after the race.
"You dream about being world champion and dedicate your whole life to it, so when it comes true it is very special.
"I may not always have been the fastest but every race I've tried my hardest."
Hayden enjoyed a 51-point advantage over Rossi, 27, in the standings after his victory in the US Grand Prix in Laguna Seca in July.
But the Italian clawed his way back into contention before taking over the lead at Estoril following Hayden's mishap.
After Sunday's dramatic decider, a philosophical Rossi said: "It was a difficult race and we had some problems.
"I made a mistake off the start and another on the slide. I don't understand why I slid but when you crash it is always a mistake.
He won, he's the best and I'm very happy for him
"It's a big emotion this year, positive and negative. We were able to gain 51 points from (the Czech GP in) Brno to arrive in front at the last race but unfortunately we lost.
"We did a lot of incredible victories but in life it is always possible to lose."
And Rossi was quick to praise Hayden, a former team mate of his at Honda in the 2003 season.
"Great congratulations to Nicky, he did a great job. He's a good guy and a great rider. He won, he's the best and I'm very happy for him."
British rider James Ellison finished the race 14th on the Tech 3 Yamaha to end the season in 18th position.
Spaniard Jorge Lorenzo won the 250cc title by finishing fourth on the Fortuna Aprilia in Valencia.
The race was won by San Marino's Alex de Angelis on the Master Aspar Aprilia as Lorenzo finished the season 17 points ahead of Italy's Andrea Dovizioso.
Britain's Chaz Davies was 21st in a wild-card ride on the Grillini Honda as fellow countryman Dan Linfoot failed to finish on the Winona Honda.
Hector Faubel won the 125cc race as his Master Aspar Aprilia team-mate and fellow Spaniard Alvaro Bautista, who was already world champion, finished fourth.
Britain's Bradley Smith was 12th on the Repsol Honda to finish his debut season in 19th.
606 COMMENT: Your views on Hayden's world title triumph
Valencia MotoGP results:
1. Troy Bayliss (Aus) Ducati 46:55.415
2. Loris Capirossi (Ita) Ducati 46:56.734
3. Nicky Hayden (US) Honda 47:04.645
4. Dani Pedrosa (Spa) Honda 47:07.480
5. Marco Melandri (Ita) Honda 47:11.721
6. Toni Elias (Spa) Honda 47:12.805
7. Shinya Nakano (Jpn) Kawasaki 47:14.744
8. Kenny Roberts Jr (US) KR211V 47:18.589
9. Colin Edwards (US) Yamaha 47:21.487
10. Carlos Checa (Spa) Yamaha 47:23.609
11. John Hopkins (US) Suzuki 47:24.779
12. Makoto Tamada (Jpn) Honda 47:25.122
13. Valentino Rossi (Ita) Yamaha 47:33.961
14. James Ellison (GB) Yamaha 48:15.428
15. Garry McCoy (Aus) Ilmor X3 +7 Laps
Final MotoGP standings:
1. Nicky Hayden (US) Honda 252pts
2. Valentino Rossi (Ita) Yamaha 247
3. Loris Capirossi (Ita) Ducati 229
4. Marco Melandri (Ita) Honda 228
5. Dani Pedrosa (Spa) Honda 215
6. Kenny Roberts Jr (US) KR211V 134
7. Colin Edwards (US) Yamaha 124
8. Casey Stoner (Aus) Honda 119
9. Toni Elias (ESP) Honda 116
10. John Hopkins (US) Suzuki 116
1. Honda 360pts
2. Yamaha 289
3. Ducati 248
1. Alex De Angelis (SMR) Aprilia 43min 52.247sec
2. Roberto Locatelli (Ita) Aprilia at 4.524sec
3. Hector Barbera (Spa) Aprilia 9.551
4. Jorge Lorenzo (Spa) Aprilia 11.366
5. Alex Debon (Spa) Aprilia 14.957
Final 250cc standings:
1. Jorge Lorenzo (Spa) Aprilia 289pts
2. Andrea Dovizioso (Ita) Honda 272
3. Alex De Angelis (SMR) Aprilia 228
4. Hiroshi Aoyama (Jpn) KTM 193
5. Roberto Locatelli (Ita) Aprilia 191
1. Aprilia 357pts
2. Honda 290
3. KTM 205
1. Hector Faubel (Spa) Aprilia 40:15.460
2. Mika Kallio (Fin) KTM at 1.764
3. Sergio Gadea (Spa) Aprilia 1.938
4. Alvaro Bautista (Spa) Aprilia 8.646
5. Lukas Pesek (Cze) Derbi
Final 125cc standings:
1. Alvaro Bautista (Spa) Aprilia 338 pts
2. Mika Kallio (Fin) KTM 262
3. Hector Faubel (Spa) Aprilia 197
4. Mattia Pasini (Ita) Aprilia 192
5. Sergio Gadea (Spa) Aprilia 160