Tunisia made the most of Zambia’s wastefulness in front of goal as they came from behind to win.
Emmanuel Mayuka opened the scoring when he blasted home a cross from the impressive Rainford Kalaba.
But Mayuka was injured when stretching for a chance to turn the ball into an empty net and moments later Tunisia scored against 10 men when Ahmed Akaichi scored from two yards out.
Tunisia improved after that and Yasine Chikhaoui headed home a late winner.
The Carthage Eagles are now on four points after two games, with Zambia on one point with one game left in Group B of the Africa Cup of Nations.
Zambia have not won a match since lifting the trophy in 2012, drawing four before this defeat, which was their first in 13 Cup of Nations games.
They could have had the game won before half-time with Kalaba firing just wide from 25 yards, forcing a save from Aymen Mathlouthi and then snatching at a chance.