Newly-crowned MotoGP champion Marc Marquez admitted he did not expect to wrap up the world title on Sunday.

The stars aligned for Repsol Honda's Marquez as he claimed a third world MotoGP championship after pole-setter Valentino Rossi and reigning title-holder Jorge Lorenzo both dramatically crashed out in a horror outing for Yamaha in Japan.

Even with Rossi out first, Marquez still needed Lorenzo to drop out of the podium places to end the title race with three rounds remaining, and that is exactly what happened five laps from the finish line, much to the 23-year-old's surprise amid wild celebrations in Motegi.

"It's an amazing feeling. I didn't expect here," Marquez said post-race.

"When I saw Rossi was out I pushed for the victory. Then I saw Lorenzo was out I made a mistake in four or five corners. It was so difficult to concentrate. To come back on the top and win at Honda and Motegi.

"I don't want to forget my grandmother who died at this time last year. I think she would be happy."

Marquez has an unassailable 77-point lead over Rossi heading into the Australian GP at Phillip Island next week.