Daniel Cousin's goal was the difference for Gabon, which lost twice to Cameroon in World Cup qualifying. Alain Giresse came out on top against Paul Le Guen in a battle of well-known French coaches.
Algeria and Nigeria both lost badly, while Ivory Coast opened by tying Burkina Faso, 0-0. On Monday, Ghana was scheduled to play Togo, which withdrew from the tournament
"It's not a big problem," Cameroon captain Samuel Eto'o said. "We have to win our next game. We controlled the game but we didn't score."
Cousin, who was just loaned from Hull City to QPR in England, took advantage of a lapse in the middle of the Lions' defense by veteran Rigobert Song and highly touted youngster Nicolas Nkoulou made a costly miss to beat goalkeeper Carlos Kameni.
Zambia and Tunisia to 1-1 in Group D's other game.