Dani Pedrosa celebrated the 250cc World Championship title for the second successive season at Phillip Island, taking a surprise victory after his only remaining rival crashed out.
Local favourite Casey Stoner started well from pole position but lost control of his Aprilia on the fourth lap, taking factory colleague Alex de Angelis down with him and handing Pedrosa the chance to take the title if he could secure victory.
Jorge Lorenzo briefly led before last year's winner Sebastian Porto took control, with Pedrosa stalking the Argentinean all the way to the final corner before emerging to take a dramatic win by just 0.027 seconds at the line for what was also Honda's 600th GP win.
Lorenzo completed the podium in a lonely third place, with Hector Barbera clinching fourth after an entertaining battle with Andrea Dovizioso and Hiroshi Aoyama.
Further back, Chaz Davies charged to 11th place for five world championship points.
250cc top ten – Australian GP:
1. Pedrosa (Honda)
2. Porto (Aprilia) +0.027secs
3. Lorenzo (Honda) +8.674secs
4. Barbera (Honda) +24.838secs
5. Dovizioso (Honda) +24.868secs
6. Aoyama (Honda) +24.872secs
7. de Puniet (Aprilia) +37.274secs
8. Locatelli (Aprilia) +47.013secs
9. Debon (Honda) +56.602secs
10. Guintoli (Aprilia) +56.747secs
11. Davies (Aprilia) +1min 9.126secs