DAMS driver Iwasa lined up second on the reversed grid behind fellow Red Bull junior Isack Hadjar, holding his place off the line.
But on the safety car restart on lap six, Frenchman Hadjar suddenly slowed with a mechanical issue that forced the Hitech driver to drop down the order before retiring.
After inheriting the lead Iwasa began building a substantial advantage over Daruvala's MP Motorsport machine before racing was again neutralised on lap 22.
Following the restart he again increased the gap to Daruvala and secured a third triumph after previous wins in Jeddah and Melbourne.
Hadjar's team-mate Jak Crawford finished third, a third podium of the Australian's rookie F2 season.
The start went smoothly, with Hadjar leading from Iwasa and Daruvala off the line, while Victor Martins passed ART team-mate Theo Pourchaire at the hairpin for eighth.
But chaos erupted once the back of the field reached the Nouvelle Chicane, with a four-car incident prompting the first safety car. Trident driver Clement Novalak made contact with Kush Maini (Campos) as the latter battled with Amaury Cordeel (Invicta Virtuosi).
DAMS’ Arthur Leclerc, Dennis Hauger (MP), PHM Racing driver Roy Nissany and Ralph Boschung (Campos) were all caught up in the incident, with Leclerc, Hauger and Novalak all forced to pit while Boschung and Nissany’s races were ended.
Novalak received a 10-second penalty for the incident, before receiving another five-second penalty for speeding in the pitlane.
Source: Autosport