Rossi, having been caught by Hayden after his early attempt to break away, had been unable to shake his former team-mate - with the pair wheel to wheel from laps 8 to 17. Rossi's reaction was to change tactics and, instead of fighting a flat out war, decided to break Hayden's rhythm with inconsistent lap times - and then by simply backing right off.
Hayden finally took the bait and went into the lead along the home straight on lap 17, but by then the chasing trio had caught the top two - and it would be Hayden who paid the biggest price. For when Rossi retook the lead on lap 19, Melandri dropped Nicky a further position by passing him under braking at the Honda hairpin.
The pair would swap positions several more times before Hayden finally found a firm advantage over the #33, but the combined effect of the squabble and Rossi's victory charge up front, meant that Hayden was now one-second from the #46 with five laps to go.
The Kentuckian did all he could to close the gap - and was clearly faster than Rossi through the sweeping Haysheds section that leads up to Lukey Heights - but Valentino excelled in other areas, with the end result that the pair were practically equal... and Nicky needed more than that.
Hayden would close the gap down slightly by the time the last lap began, but Rossi was always just out of reach - however, behind the top two, a thrilling battle for third was still raging and would go down to the flag.
Having been crawling all over the back of Melandri's Movistar Honda for several laps, Checa had slipstreamed past the Italian for the final podium position into turn one of the final lap - but Melandri retook the place at the Honda hairpin.
Marco then made his machine as wide as possible through the following corners, and was still ahead as the pair made their way through the final sequence of fast left hand turns that leads to the finish. But it was then that Checa, who had already shown a considerable top speed advantage, tucked into Melandri's slipstream and stole a one-day-late Birthday present by pinching third by just 0.017secs at the flag.
But four-seconds earlier Rossi had racked up his fifth consecutive Australian Grand Prix victory and handed Yamaha a clean sweep of the 2005 world championships with the Riders', Teams' and now Manufacturers' crowns all going to the Japanese company in its 50th anniversary season.
Hayden, although unable to build on his solitary MotoGP victory to date, could take considerable pride from his second podium in a row - and the fact that his runner-up position, combined with the non-scores for Biaggi and (non-starter) Loris Capirossi, means that he is now level with Melandri for second in the championship, with two races to go.
10secs behind Marco on track today was team-mate Gibernau, whose pre-race fears proved correct, while Edwards was an equally lonely sixth after Alex Barros
suffered a worrying high-speed fall from that position on lap 23.