Corsi was involved in a race-long battle with Belson Derbi's Joan Olive, as those involved in the tussle for the win gradually dropped out of the running.
In the end it came down to Corsi vs. Olive, although the last lap was more a question of Corsi holding his nerve than duking it out with his Spanish rival. He was up to the task, and passed the chequered flag three tenths of a second ahead of Olive.
Continuing the team's fine form from Jerez, both Jack&Jones WRB riders placed on the podium. Nico Terol earned a second successive rostrum finish in third place, taking the fledgling team further up the group standings.
Heading the group competing for fourth place, Stevie Bonsey achieved his best ever Grand Prix result in the third race of his sophomore season.
The American started from second on the grid, and his weekend is a positive boost for both him and his DeGraaf Grand Prix Aprilia team, who also occupied the next place down through Danny Webb.
Reigning world champion Gabor Talmacsi experienced a continuation of his difficulties from the opening two races, a podium spot still eluding him in his title defending year. He rounded off the top six, ahead of Mike di Meglio, Stefan Bradl, Sergio Gadea and Sandro Cortese.
Battling for victory, Polaris World's Bradley Smith crashed out in the latter stages of the race, whilst other spectacular tumbles befell Raffaele de Rosa and Karel Pesek.
Race results - Estoril:
1. Corsi (Aprilia)
2. Olive (Derbi) +0.299secs
3. Terol (Aprilia) +6.355secs
4. Bonsey (Aprilia) +14.793secs
5. Webb (Aprilia) +15.532secs
6. Talmacsi (Aprilia) +15.868secs
7. di Meglio (Derbi) +15.875secs
8. Bradl (Aprilia) +17.887secs
9. Gadea (Aprilia) +18.123secs
10. Cortese (Aprilia) +22.613secs
21. Redding (Aprilia) +1min 7.908secs
Smith (Aprilia) DNF