However, Haga's charge up the order would come to a dramatic halt just a lap later when, as he was pushing hard to catch Byrne, his bike got away from him, man and machine sliding forlornly off the circuit as the field swept past. Despite his best efforts, Haga couldn't get going again and was forced to concede.
With Yamaha immediately notifying Spies of Haga's misfortune, attention turned to the front as Biaggi continued to put pressure on the American.
A series of quick laps at the start of the race had helped the pair to put air between themselves and Rea, Biaggi mirroring Spies, even if he never looked close enough to wrest the position off him.
However, when both riders began to experience a slight dip in pace at the half-way stage, it would prompt Rea and Byrne to get back in contention, the duo making it a four-way battle by lap fourteen.
Despite the added attention of his rivals, Spies would ultimately benefit from Biaggi and Rea's feuding, eking out his margin to just over a second.
With Rea's best opportunity to pass down the home straight being scuppered by the Aprilia's superior straight-line speed, it took an error from Biaggi on lap 16 to allow the Ten Kate Honda man through into second position.
Giving him a shot at trying to catch Spies, Rea was almost two seconds behind the leader as they entered the latter stages of the race. However, the gap wouldn't come down, with Biaggi instead slipstreaming past into second place again on lap 19. Not to be outdone, Rea struck back on the penultimate revolution with a daring pass on the Italian at turn two.
It meant Spies was free to ease to the chequered flag with a 1.6sec advantage over Rea, prompting jubilation in the Yamaha garage as they now stand on the verge of winning their first ever World Superbike title.
Having been unable to respond to Rea's decisive attack, Biaggi was instead hounded across the finish line by an inspired Byrne, who put in one of his most convincing rides of the season to come home fourth for Sterilgarda Ducati. The result also means he moves up to eighth in the standings at the expense of Tom Sykes, who has withdrawn from the final round with a shoulder injury.
Fabrizio came home a quiet fifth having been outshone by the privateer Ducati of Byrne, while Leon Camier put in a fine performance to claim sixth on the Aprilia after working his way up from 13th position on the grid.