With Andre Onana on the bench, and watching on, Gambia were arguably the better side in the first half, and created more than one excellent chance, but their profligacy meant they were unable to find a way through.
An exceptional save from Fabrice Ondua, in for his cousin Onana, was required to keep the scores level heading into half-time, as he denied Modou Barrow on the spin with superb reactions.
After half-time, Cameroon finally carved out a gilt-edged chance, as a deep cross found Georges-Kevin N'Koudou free at the back post, but his rasping drive rattled the crossbar and bounced clear.
The momentum kept flowing and Karl Toko-Ekambi headed home a superb N'Koudou delivery to break the deadlock. But Gambia kept pouring forward, and in the 71st minute, they shockingly levelled through Ablie Jallow, as he volleyed home a superb delivery to leave Ondua rooted.
And they added a deserved second just minutes later, leaving their players in tears, as Ebrima Colley found the back of the net after being slipped through one-on-one.
But within a minute of the restart, Cameroon equalised, as James Gomez scored a heartbreaking own goal while trying to cut out a cross. And Cameroon appeared to steal it late on as Christopher Wooh powered a header into the bottom corner from an N'Koudou corner.
In the 94th minute, Gambia thought they had an equaliser through Muhammed Sanah, but the ball clearly came off his hand before nestling in the bottom corner. He was subsequently booked, one of the final actions of a truly astonishing end to the game.