- Marc Marquez wins Japanese MotoGP
- Clinches third world title
- Closest rival Valentino Rossi crashes out
- Andrea Dovizioso second in Japan
The Repsol Honda rider has an unassailable 77-point lead over Rossi in the championship with three rounds still remaining after his triumph at Motegi, the home circuit for his team's manufacturer.
Italian legend Rossi had started from pole on his Movistar Yamaha and was involved in an exciting duel with Marquez until an early trip to the gravel ended his chances of a 10th world title.
Rossi's teammate Jorge Lorenzo, the reigning world champion, was left as the only man who could deny his fellow Spaniard Marquez the title, but while in second place, he too made a painful exit.
It left Marquez to ride to his fifth win of the season and a third world title in four years in the premier class of motorcycling, still shy of his 24th birthday.
With the Yamaha challenge over, Andrea Dovizioso took a fine second for Ducati with Maverick Vinales of Team Suzuki completing the podium with another fine ride.
But all eyes were on Mallorcan hero Marquez, who admitted he had not expected to clinch the championship, the reality only sinking in after Lorenzo exited in dramatic fashion.
"When I saw Rossi out I thought 'ok, the old style can come back and I'll go for the victory!' Then Lorenzo crashed and I missed a lot of gears when I realized what it meant," he told the official MotoGP website.
Losing the crown to Lorenzo in 2015 as a two-time reigning champion had also acted as a big motivation for Marquez this season.
"It was a big price I paid -- losing a title last year -- to learn what I know now. I felt more pressure this year and it was hard to manage throughout the season," he admitted.
It is the fifth world title for Marquez, who won earlier championships in the 125cc and Moto2 classes before graduating to MotoGP with such success at a tender age.