Holding station in third, Biaggi looked set to stay there, only for him to come under intense pressure from former team-mate Leon Camier aboard the FIXI Crescent Suzuki during the latter stages
The Briton had spent several laps trying to get on the tail of the Aprilia, but his first attempt at passing on lap 19 nearly ended in disaster when he dived for a gap and made contact with Biaggi. Despite the fairly solid impact, both riders stayed upright, but while Camier resumed his efforts to grab third, a mechanical problem on the penultimate lap would ultimately lead to a bitter retirement.
Up ahead, Laverty came into the last lap facing increasing pressure from a charging Rea, whose pace in the final revolutions would see him crawling over the back of the Aprilia as they entered the home straight for the last time.
Ultimately though Rea wouldn't have time to challenge Laverty, the Irishman holding on to secure a long-awaited first victory as an Aprilia rider, a result that also puts the Italian marque on the cusp of the manufacturers' title.
Behind Rea, Biaggi came across the line in what became a very lonely third, well ahead of Sylvain Guintoli and Carlos Checa
in fourth and fifth, the outgoing champion fighting back after dropping as low as 14th with a mistake on lap two.
Ayrton Badovini completed one of his better results of the season in sixth place, ahead of newly-signed Kawasaki rider Loris Baz and Michel Fabrizio.
Fresh from his stunning run to fifth in race one, Brett McCormick completed a successful day with a ninth place finish, just ahead of Effenbert Liberty Ducati team-mate Lorenzo Lanzi.
With all 15 finishers scoring points, John Hopkins, Lorenzo Zanetti, David Salom, Alexander Lundh and Norino Brignola all received digits for reaching the chequered flag.