Trevor Mukendi got the goal on 61 minutes at the Stade de Municipal in Dolisie, Congo-Brazzaville.
A loss for Leopards would have ensured Pirates a place in the last-four of the continental competition.
Nevertheless, Eric Tinkler's men share the Group B summit with Zamalek on nine points apiece after four games - five points in front of Leopards, and eight ahead of Tunisian outfit CS Sfaxien.
Bucs eliminated Sfaxien 2-0 in Soweto on Saturday thanks to strikes either side of the break from Thabo Rakhale and Menzi Masuku.