Sebastien stormed to a perfect 1-1 sweep of the premier class en route to his first ever MX1 victory. Josh Coppins came closest to the French rookie in both races, while CAS Honda's Mike Brown completed the overall podium after a pair of fourths.
Coppins thus increased his huge world championship lead to 107 points over Suzuki's Steve Ramon, who had a difficult weekend in Italy, while Pourcel's victory has pushed him up to third in the standings.
In the MX2 class, defending world champion Christophe Pourcel had only beaten Antonio Cairoli once prior to the Italian's second home round - but the Frenchman rose to the considerable challenge and beat Cairoli to the overall with victory in moto two.
Yamaha star Toni caught and passed Pourcel midway through the first race, but was unable to repeat the feat in the deciding second moto. Cairoli suffered a poor start and by the time he reached second was 10 seconds behind Pourcel, forcing the Italian to admit defeat. KTM's Tyla Rattray produced two solid third places to claim that position on the end of day podium.
In the world championship standings, Cairoli and Pourcel remain 102 points apart, due to their identical moto finishes, while Rattray reinforced third ahead of team-mate Tommy Searle and Pascal Leuret.
The 2007 grand prix stars will now have a weekend to recover from the roasting Faenza heat before heading for the Grand Prix of the Czech Republic, on July 29.