Coton Sport of Cameroon went top of the Group B standings after beating Sudan’s Al Hilal 1-0 in Garoua in the day’s other tie.
A ninth-minute goal from Mohamed Barakat in Harare moved Al Ahli, seeking a record sixth win in Africa’s top club competition, on to 10 points from their four group matches.
They will be confirmed as semi-finalists if ASEC Abidjan fail to beat Egypt’s Zamalek in Sunday’s Group A match in Ivory Coast.
Barakat squeezed home a shot after a swift attack from the Cairo giants at Rufaro stadium. Al Ahli had two more efforts disallowed.
Hosts Coton Sport, playing in the league phase for the first time, took charge of their group after Baba Ousmaila scored a late winner.
Al Hilal, who were semi-finalists last year, had Alaeldin Gibril sent off midway through the second half as they slipped to third in the standings.
Coton Sport have a one point lead over Nigeria’s Enyimba, who have a difficult away match at TP Mazembe Englebert of the Democratic Republic of Congo in Lubumbashi on Sunday.