Mane, who also scored last Wednesday when Senegal beat Guinea Bissau 2-0 at home, netted with eight minutes remaining to ensure they maintained their 100 percent record in Group I where they are guaranteed a top-two finish and therefore a place at the finals in Cameroon in January 2022.
Senegal have 12 points from four games, six ahead of second-placed Congo and nine ahead of Guinea Bissau in third spot.
Senegal were runners-up at the last Cup of Nations tournament in Egypt in 2019.
Mane’s Liverpool team mate Naby Keita scored for Guinea as they stayed top in Group A with a 1-1 draw away in Chad.
Ahmat Abdaraman equalised just before halftime for Chad, who collected their first point after three successive defeats.