كتب : Hatem Maher
A brace from striker Julien Viale either side of the interval gave them a precious victory.
Mickael Colloredo scored Nimes' sole goal nine minutes past the hour mark.
Egyptian winger Abou-Mosallam, who created Ajaccio's goal in last week's 1-1 draw with Clermont Foot, played full 90 minutes for the third successive game after recovering from injury.
The former Ahli man, who joined Ajaccio on a six-month loan from Strasbourg, had a powerful shot from just outside the area blocked by Nimes keeper 12 minutes before the final whistle.
Ajaccio remained 17th in the 20-team table but became five points clear of the relegation zone.