By the halfway stage, Tamada had passed the five-times world champion - and one lap later created a Camel Honda one-two by blasting past Hayden - while Rossi was about to commit a rare, and very costly error...
The Italian was holding an 'easy' fourth, 2secs clear of the fading Barros, when he lost the front of him M1 and slid into the Brazilian gravel. Rossi rushed to remount, but the damage had been done and he was forced to retire for the first time since Brno 2002, when a tyre failed, he hasn't crashed out of a race since Mugello 2001!
The Doctor's departure left the top three - Biaggi, Tamada and Hayden - to dispute victory, with Tamada looking by far the most threatening as he crawled all over his Roman team-mate, while Hayden was positioned ready to pounce should the yellow machines stumble.
After sizing up Biaggi for eight laps, Tamada finally hit the front with four to go; the Japanese seeming to sense he had the legs on Biaggi's Michelin machine and looked keen to break away before any last lap mayhem.
Whatever the plan – it worked: Tamada carried a commanding a 1.1secs lead onto the last circulation, with Hayden a further 2.4secs back for a safe third.
Even with the potential aid of a slipstream, Max simply couldn't close the deficit in the remaining 4.9kms and would cross the line 2secs adrift of a jubilant Tamada, who erupted in celebration at achieving his – and Bridgestone's – first ever MotoGP victory.
Biaggi's subdued body language contrasted sharply with that of Tamada's – and indeed Hayden's, the American appearing genuinely pleased for the Japanese – but when the disappointment of defeat subsides, the four-times 250cc world champion will surely take comfort from the fact that he's now right back in title contention, 13-points behind Rossi and Gibernau.
6secs behind Hayden was Capirossi, the Italian equalling Ducati's best finish of the year (in the twin-pulse's second race) after narrowly holding off the Hondas of former team-mate Barros and Texan Colin Edwards for the second half of the GP. By contrast, Capirossi's team-mate Troy Bayliss, using the four-pulse, fell on lap 4 after losing the front.
Kenny Roberts eventually brought his Suzuki home as second best Bridgestone machine, but was a distant seventh - ten-seconds behind countryman Edwards and four ahead of the top Yamaha of Norick Abe (eighth). Kawasaki's Shinya Nakano and Rossi's team-mate Carlos Checa completed the top ten.
Further back, John Hopkins survived a last lap collision with Kawasaki's Alex Hofmann - and then a tyre wall - to take the final world championship point in 15th.
Full results to follow...
Rio Grand Prix:
7. Kenny Roberts
19. Kurtis Roberts