Aaron Boupendza's first-half finish was the difference as Gabon edged past Africa Cup of Nations debutants Comoros in Group C.
Gabon forward Louis Ameka latched on to a loose ball before playing in Boupendza to strike from a tight angle after 16 minutes.
In the second half Gabon's Denis Bouanga twice forced Comoros keeper Ali Ahamada into fine reaction saves.
Comoros created little in response as the West Africans cruised to victory.
Gabon now sit joint-top of Group C after Sofiane Boufal's 83rd-minute strike had earlier handed Morocco a narrow win over Ghana.
Comoros, the Island nation in the Indian Ocean who qualified ahead of Kenya and Togo, dominated proceedings before Gabon's opener against the run of play.
But once the two-time quarter-finalists went in front it as one-way traffic, even without star player Pierre-Emerick Aubameyang who missed this match after testing positive for Covid-19.
Comoros face Morocco on Friday (16:00 GMT) before Gabon play Ghana (19:00 GMT).