Rossi's reaction was to try even harder, attempting to pass on the inside at the Spoon curve, but Biaggi 'leaned' on the youngster once again and he was forced to submit – briefly losing a place to Ukawa in the process.
The pass was finally made along the start/finish straight with Rossi chopping sharply across the nose of Biaggi's machine and then 'hand signalling' his displeasure at Biaggi's previous manoeuvre(s).
Rossi, now released, soon passed Nakano and then leader McCoy, again going into the Spoon curve, so that the order by lap 8 was Rossi, from McCoy, Biaggi and Haga.
Biaggi moved past McCoy in pursuit of Rossi, while Rossi began to build a small lead.
Meanwhile Noriyuki Haga continued to charge and was up to third by lap 11 – before crashing, for the third time this weekend, after losing control of his Red Bull Yamaha and sliding into the gravel.
Haga's exit allowed Ukawa to close on Biaggi and the two began a thrilling duel, passing and re-passing each other, while Rossi built his lead to 1.5secs, with McCoy fourth, Abe fifth and Nakano sixth.
Two laps later Ukawa found a way past Biaggi at the chicane and immediately set off in hot pursuit of leader, and fellow Honda rider, Rossi. Biaggi's slid continued with McCoy also passing the Italian for third and then Ukawa for second into turn one at the beginning of lap 17.
Meanwhile, World Champion Kenny Roberts Jr.'s nightmare weekend continued, as he languished down in eighth on the Telefonica MoviStar Suzuki. This would soon become seventh however, when 500cc rookie Ukawa spectacularly high-sided as he accelerated out of the chicane.
As the unfortunate Japanese rider and his Repsol Honda slid down the track, the pursuing Biaggi was forced to slow allowing both Nakano and Abe to pass the Italian.
To the order on lap 18 of 21 was therefore: Rossi 3.508secs ahead of McCoy, followed by Nakano, Abe and Biaggi.
Abe however, soon past Nakano at the 130R, with Biaggi dropping the Gauloises Yamaha rider back a further place as he too crept by at the chicane, and set off in pursuit of Abe and the final podium position.
Biaggi shadowed the Japanese rider until the very last lap when moved into third and immediately began pressuring McCoy for second. McCoy absorbed the pressure and held off Biaggi to the line, while Valentino Rossi won at a track where his previous best finish was just eleventh.
Full classification to follow…
1. Rossi 44mins 51.501secs
2. McCoy +0.724secs
3. Biaggi +0.956secs
4. Abe +1.176secs
5. Nakano +2.256secs
6. Barros +14.515secs
7. Roberts +22.876secs
8. Capirossi +28.732secs
9. Criville +34.478secs
10. Checa +53.765secs
11. van den Goorbergh +58.688secs
12. Aoki +1min 17.338secs
13. Haslam +1min 17.681secs