Enyimba top their CAF Confederation group after match day 1 following their 2-0 home over Djoliba, while Williamsville pipped visiting CARA Brazzaville 1-0 on Sunday.
The NPFL club scored two second half goals through Isiaka Oladuntoye in minute 48 and a penalty by Stanley Dimgba in the 81st minute sealed the win for Enyimba.
It was the first group C game and the host ensured they made the best out of opening at home in Calabar.
In the other group game, Ivorian side WAC also picked three points following a 1-0 win over CAR from Congo, but sit second in behind the Aba Elephants on inferior goals.
Matchday 2 comes up on May 16 and it will be the battle between first and second at the Stade Alphonse Massemba-Débat in Brazzaville.