The 21-year-old needed to beat Valentino Rossi to wrap up the crown three rounds early, and was assured of the title when the Fiat Yamaha rider suffered braking problems on his second bike - after all riders were forced to pit due to a drying track - and finished just 13th.

Stoner and Rossi had battled for the lead before their pit stops, after which Stoner's team-mate Loris Capirossi scored his third Motegi victory in a row - helped by a perfectly timed bike change - ahead of Kawasaki's Randy de Puniet and Honda Gresini's Toni Elias.

Casey is the second youngest premier-class world champion in the history of the sport, after Freddie Spencer in 1983, while Ducati is the first non-Japanese manufacturer to win the premier-class crown since Phil Read handed another Italian factory, MV Agusta, its final 500cc World Championship in 1974.

More to follow...