Promoting Biaggi and Haga up to second and third, attention turned to whether the Japanese rider could get past his sparring partner and launch a challenge on Spies.
Just as he showed at Imola though, Biaggi was proving a difficult obstacle for Haga to overcome, the Aprilia's superior pace out of the corners negating the Ducati's seemingly better braking ability.
Indeed, with Spies just beginning to creep away out front, Haga's mid-race assault would see him get an overlap on Biaggi into the Adelaide hairpin on numerous occasions, only for the RSV-4 to hold its position on the exit of the bend.
Running out of time to make his move, it was Haga's trademark tight line into the 180 left-hander that would eventually see him past Biaggi, the Italian leaving a Ducati sized gap on lap 17 to allow Haga through into second position.
An attempt to fight back at Adelaide hairpin the very next lap would see Biaggi simply run on after out-braking himself, freeing up Haga to chase down Spies, whose capitalisation of the situation had seen him extend his lead to 1.3secs.
With just six laps remaining, Haga, cheered on by team manager Davide Tardozzi from the pit wall, immediately signalled his intentions with a series of quick laps, most notably his record-breaking effort on the penultimate revolution. Nonetheless, with Spies also visibly pushing hard to repel any last lap challenge, it was evident that the American would need to make an error to allow Haga through.
Remarkably, however, this is exactly what occurred when Spies missed his apex into 180 and was forced to take a wide line around the bend. Haga pounced on the error, slipping up the inside to snatch the lead of the race.
Nonetheless, Spies kept his cool to cut back up the inside of Haga on the exit of the corner, his superior drive out of the bend eking him back ahead as they sprinted into the high-speed Imola right-left.
Having survived one scare already, Spies and Haga were left almost side-by-side on the long run down to Lycee, but with the Yamaha getting through the bend first, there was no chance for his rival to take back the position.
A 13th win of the season for Spies, the result moves him back into the lead of the standings by a mere two points with just three races remaining this now.