"It was a difficult game for us," Cameroon coach Paul Le Guen said. "We still need to improve in a number of areas. We got the victory we wanted and that is what is important."
Cameroon trailed early on a goal by Jacob Mulenga, but the Lions rallied on goals by veterans Geremi and Samuel Eto'o to go ahead 2-1.
Chris Katingo's penalty kick for Zambia tied the score in the 80th minute.
In Sunday's first game, Tunisia and Gabon played to a 1-1 tie, leaving Gabon in first place with four points.
Only Ivory Coast and defending champion Egypt have clinched berths in the quarterfinals.