Cameroonian Jean Francis Ebele Dipita gave Horoya a first-half lead they held until 11 minutes from time when Ben Malango equalised in the west African city. Mazembe are the second most successful club in CAF competitions with 10 titles -- nine less than Al Ahly of Egypt -- while Horoya won the now defunct African Cup Winners Cup in 1978.
Emeka Atuloma scored his second goal this season in the secondary African club competition with 19 minutes remaining to secure maximum points in southern city Port Harcourt. Rivers, the only survivors from a four-club Nigerian challenge for 2017 CAF titles, began their mini-league campaign with a 3-1 loss at Club Africain of Tunisia.
FUS remain top of Group A, but only on goal difference from Club Africain, Rivers and Kampala Capital City Authority of Uganda with each club having three points.
Kampala, the first Ugandan club to qualify for the group stage of a CAF competition, came from behind Tuesday to edge Club Africain 2-1 in the Ugandan capital.
Ivorian Cheick Moukoro struck seven minutes from time to give Al Hilal Obeid of Sudan a 1-0 home victory over previously unbeaten Zesco United of Zambia in Group C.
Zesco are among the favourites to win the competition having made a big impact in Africa last year by reaching the CAF Champions League semi-finals against the odds.
Smouha of Egypt defeated Recreativo Libolo of Angola 2-0 in Alexandria in the same group to go top on goal difference in another section where all four clubs have three points.
After Ahmed Raouf scored on 12 minutes in the ancient Mediterranean city, Smouha had to wait until stoppage time before clinching victory through an Islam Mohareb goal.
South African outfit SuperSport United lead Group D on goals scored with Mazembe second. Each club has four points, two more than Horoya, while CF
Mounana of Gabon are pointless.
Matchday 3 is scheduled for June 2-4.