Casey Stoner capped a memorable 26th birthday by clinching his second MotoGP title with victory at his home race.
Australian Stoner only had to finish in the top six to be crowned champion after
with a hand injury suffered in a crash in Sunday morning's warm-up.
Jorge Lorenzo was ruled out of the race
But he cruised to victory at Phillip Island for the fifth consecutive year.
Stoner told BBC Sport: "To wrap it all up at my home race and on my birthday is perfect."
Italian rider Marco Simoncelli finished second, with compatriot Andrea Dovizioso in third.
Repsol Honda rider Stoner last won the title for
and he added: "We have been thinking about this all week but, to be honest, I didn't think we had a chance of taking the title today.
Ducati in 2007.
"Jorge has been so fast and consistent all season but he had a crash with quite a serious injury so my thoughts are with him.
"That gave me the opportunity but the track threw everything at us with wind, rain and hail. I wanted to seal it today and we did that.
"The momentum was with us and it was our title to lose."
Lorenzo was passed unfit to race after losing the tip of the ring finger of his left hand, leaving Stoner to make a clean start to lead through turn one.
Nicky Hayden shot through into second with Simoncelli third.
All-time MotoGp/500cc wins
Valentino Rossi made up seven places on the opening lap to move into the top six as Stoner opened up a two-second lead by the end of lap two.
Simoncelli barged past into second with a slick move through the final corner before Dovizioso overtook Hayden to move into third.
Stoner was nearly six seconds clear when light rain started to fall over some of the circuit on lap 10 but none of the riders entered the pits to change bikes to a wet setup.
Dani Pedrosa eased past Dovizioso with 15 laps remaining and Rossi was soon able to overhaul team-mate Hayden to re-enter the top six.
Rossi charged past Alvaro Bautista a lap later but lost the front end in the drizzle at turn 10 and crashed out.
Dovizioso was able to muscle back past team-mate Pedrosa to take third before the rain returned with three laps to go.
Bautista was caught out in the wet and Cal Crutchlow and Hiroshi Aoyama then both also slipped off.
Dovizioso briefly took advantage of the change in conditions to pass Simoncelli for second before Simoncelli came back through.
Stoner hails 'special' Championship win
Stoner survived a scare of his own before easing off to bring his Honda home for a memorable win which sealed his second title.
Australian MotoGP race result:
1) Casey Stoner (Aus) Repsol Honda 42'02.425
2) Marco Simoncelli (Ita) Gresini Honda 42'04.635
3) Andrea Dovizioso (Ita) Repsol Honda 42'04.879
4) Dani Pedrosa (Spn) Repsol Honda 42'15.585
5) Colin Edwards (USA) Tech 3 Yamaha 42'33.311
Moto2 race result:
1) Alex De Angelis (RSM) Motobi 39'44.774
2) Stefan Bradl (Ger) Kalex 39'46.132
3) Marc Marquez (Spn) Suter 39'51.136
125cc race result:
1) Sandro Cortese (Ger) Aprilia 34'49.670
2) Luis Salom (Spn) Aprilia 35'03.242
3) Johann Zarco (Fra) Derbi 35'03.981