The Super Eagles used a strong second half to ease past fellow West Africans 4-1 in their group C encounter in Kagali.
The bronze winners in the 2014 version that took place in South Africa dominated the first half but repeatedly could not get past the Mena off side trap that worked flawlessly.
Nevertheless both teams had their chances with Osas Okoro repeatedly coming close and Ezenwa being tested at least twice.
The second half saw a brand new Nigeria and within 30 seconds of resumption Osas Okoro had put the Eagles up 1-0. Despite a brave rally led by Adebayor, Chisom Chikatara would double the lead in the 75th minute on his way to his hat trick.
Adebayor struck back for the Mena with arguably the goal of the tournament when his bomb whizzed past Ezenwa in the 81st minute. However while they were still celebrating, the MOM Chisom Chikatara, set up by Osas Okoro, slammed in his second goal.
That let the air out of Niger because in the last minute of the game Chikatra added his third, completing the rout.
Nigeria now top Group C ahead of Tunisia and Guinea who played to a 1-1 draw earlier on in the day..