A stunning long-range shot by full-back David Alvarez in stoppage-time sent Equatorial Guinea to top spot in Group A and the small country into delirious celebration.
Iban Iyanga, better known by his footballing name Randy, headed home the first goal of the game just after the hour mark to set up the win but home hopes seemed dashed when Senegal equalised in the 89th minute through Moussa Sow.
Alvarez then hit a spectacular drive from outside the penalty box to win the match and ensure one of Africa's smallest countries will play in next week's quarter-finals.
Ranked 108 places below Senegal, Equatorial Guinea's controversially-assembled side - all born outside the country - fought for every ball on a rain-soddened pitch.
Senegal striker Demba Ba had three good opportunities in a 12-minute spell in the first half but missed them all. A stinging shot from Guirane Ndaw was also well-saved by Equatorial Guinea's Brazil-born goalkeeper Danilo.
