Cousin scored early in the first half and the Gabonese survived numerous goalmouth scares to record only their second victory in four appearances at the biennial continental showcase. Cameroon, four-time champions and twice runners-up, entered the game as hot favourites to secure maximum points having comfortably beaten Gabon twice in the qualifers.
"We are very pleased we got a win in the first game. Our system worked well and technically we were very good," said Gabon coach and former France star Alain Giresse. "Even if we finish second in this group we will be happy. What we want is to qualify for the quarter-finals," he said of a mini-league completed by Tunisia and Zambia.
Cameroon captain Samuel Eto'o displayed no signs of panic as the jinx affecting World Cup qualifiers at the Nations Cup continued with Algeria and Nigeria also losing their opening game and the Ivorians drawing. "Losing today is not a big problem but we have to win our next game against Zambia on Sunday. We controlled the match but could not find the net," lamented the three-time African Footballer of the Year.
Veteran Cameroon central defender Rigobert Song created history when the match kicked off by becoming the first footballer to play in eight Nations Cup tournaments. The 33-year-old from Turkish club Trabzonspor overtook current Egypt captain Ahmed Hassan and two retired stars, compatriot Hossam Hassan and Ivorian Alain Gouamene.
Cameroon started by taking the game to Gabon and Achille Emana was unlucky after eight minutes when his shot was pushed on to the post and away for a corner by goalkeeper Didier Ovono. But the game took a dramatic twist on 17 minutes when the Indomitable Lions failed to clear a cross and Cousin darted through to push the ball wide of goalkeeper Iddriss Kameni and give Gabon a shock lead.
Going in front boosted the confidence of outsiders Gabon and they retained the advantage until half-time with reasonable comfort as Cameroon star Samuel Eto'o failed to make his expected impact. Geremi Njitap did worry Ovono with a free-kick and Eto'o finally came to life just before the break with a dribble past several defenders, but the ball was eventually cleared.
Cameroon's French-born coach Paul le Guen made a change in central midfield for the second half, introducing Tchoyi Somen for Landry Nguemo and the new face was soon making his presence felt. Ovono, who once battled to make a living playing in El Salvador, was in inspired form and did well to parry a close-range header off a corner and foiled Eto'o when the Inter Milan striker seemed poised to equalise.
Frustration crept into the game as Cameroon continued to dominate possession only to be thwarted by Ovono, who used his feet to push away a close-range Emana drive at the expense of a corner.
Gabon time wasting cost midfielder Stephane Nguema and striker Roguy Meye yellow cards with the latter booked for taking too long to leave the field when substituted by Pierre-Emerick Aubameyang. Ovono came to the rescue again as time ticked away, touching a dipping free kick from Njitap over the crossbar and the resultant corner ended with Rigobert Song blazing over.