A stunning solo goal from Piqueti was not enough for Guinea Bissau as Cameroon came from behind to win 2-1 and take pole position in African Nations Cup Group A.
Piqueti powered through the Cameroon defence to give his side an early lead.
But Sebastien Siani equalised and Michael Ngadeu-Ngadjui struck what proved to be the winner as Cameroon clinched the first win of Group A.
The Indomitable Lions, who have four points, next play hosts Gabon in Sunday's final group game, while Guinea Bissau meet Burkina Faso.
Cameroon went close as Clinton Njie pulled the ball down at the back post, but Mamadou Cande blocked and Juary Soares blocked from Vincent Aboubakar.
Piqueti launched an attack from deep inside his own half, lifting the ball over Collins Fai before chasing on to it.
He surged by his would-be tacklers as Ngadeu-Ngadjui backed off before cutting to his right and rifling in an unstoppable shot.
Guinea's speed on the break troubled Cameroon, but Ambroise Oyongo's late intervention denied Frederic Mendy.
Benjamin Moukandjo shot into the ground from Aboubakar's knock-down and Jonas Mendes saved as Cameroon went close again.
Next Njie burst down the left and cut the ball back for Aboubakar in space. But the striker spurned the opportunity.
A low Moukandjo shot went wide from the edge of the area before Guinea went close again.
Mendy hassled Oyongo, stole the ball and lifted it towards goal as Fabrice Ondoa rushed out, but Ngadeu-Ngadjui cleared the ball off the line.
Ondoa saved from Mendy before Cameroon equalised. Guinea failed to clear, Moukandjo teed-up Siani who powered a low shot into the bottom corner.
Cameroon continued to press and had a second when Christian Bassogog ran down the right and the ball fell for Ngadeu-Ngadjui. He blasted the ball in at the near post.
Substitute Robert Ndip Tambe dragged a shot wide across goal in stoppage time as Cameroon celebrated victory.