Casey Stoner resisted enormous pressure from Valentino Rossi to win his home grand prix at Phillip Island for the third consecutive year - but second stretched Rossi's championship advantage to 38 points after Jorge Lorenzo crashed out.
The most significant moment of the Australian Grand Prix - and perhaps the 2009 title battle - occurred within yards of the start, when Lorenzo (Yamaha) tagged the rear of Nicky Hayden's Ducati going into Doohan curve.
That unbalanced both riders, and while Hayden speared through the gravel but was able to stay upright and limp to the finish, Lorenzo fell and could only watch as his team-mate Rossi moved a massive step closer to another title. The Spaniard escaped from the high speed incident with grazes to his hand and face.
Dani Pedrosa had yet again thrust his Honda into the lead at the start - and although Stoner passed him into MG corner, the Spaniard came straight back at the Ducati and led at the end of lap one.
Both Stoner and Rossi overtook Pedrosa next time around, though, and then pulled away to start their own battle.
The last two world champions ran less than a second apart for the first 20 laps, with Stoner inching away at first before being reeled in. Rossi tried a series of passing attempts in the first half of the lap, while Stoner had the speed to pull clear in the final corners.
Every time Stoner managed to put clear air between them, Rossi clawed back onto his tail - both riders sliding their bikes to the limit. Finally in the closing stages Stoner managed to escape - with a blistering last lap extending his winning margin to 1.9s, by far his biggest lead of the race.
Pedrosa was left in a lonely third, shaking off early pressure from Gresini Honda's Alex de Angelis, who later had to focus on the closing Colin Edwards - the Tech 3 Yamaha rider having battled clear of the early seven-bike battle for fifth. Edwards' team-mate James Toseland's race was ruined by his second jump-start penalty of the year.
Andrea Dovizioso took sixth on the second Honda, ahead of the duelling Marco Melandri (Hayate Kawasaki) and Randy de Puniet (LCR Honda), and Mika Kallio's Pramac Ducati.
A fast start saw Toni Elias briefly in the top five, but he was ultimately shuffled back to 10th on the second Gresini Honda.
Suzuki's miserable weekend ended with 11th and 12th, both its riders having had to fight hard to get away from Scot Honda's Gabor Talmacsi.
Pos Rider Bike Time/Gap 1. Casey Stoner Ducati 40m56.651s 2. Valentino Rossi Yamaha + 1.935s 3. Dani Pedrosa Honda + 22.618s 4. Alex de Angelis Gresini Honda + 32.702s 5. Colin Edwards Tech 3 Yamaha + 35.885s 6. Andrea Dovizioso Honda + 38.482s 7. Marco Melandri Hayate Kawasaki + 44.451s 8. Randy de Puniet LCR Honda + 44.941s 9. Mika Kallio Pramac Ducati + 54.345s 10. Toni Elias Gresini Honda + 1m01.205s 11. Chris Vermeulen Suzuki + 1m05.417s 12. Loris Capirossi Suzuki + 1m05.950s 13. Gabor Talmacsi Scot Honda + 1m17.951s 14. James Toseland Tech 3 Yamaha + 1m17.985s 15. Nicky Hayden Ducati + 1 lap Retirements: Jorge Lorenzo Yamaha 0 laps