Nigeria beat Guinea-Bissau 2-0 in Garoua to become the only side at the Africa Cup of Nations to win all three group games.
After making eight changes to the side that beat Sudan to seal their last-16 place, Nigeria took time to warm up.
Umar Sadiq opened the scoring shortly after the break following a cross from striker partner Kelechi Iheanacho.
Captain William Troost-Ekong sealed the win after tapping into an empty net after fine work by Moses Simon.
Three-time champions Nigeria had already topped Group D and knew their round of 16 clash on Sunday would be in Garoua, where they have played all their games so far.
They will have to wait until Thursday night to find out which of the best third-placed sides they face from either Group B, E or F.
Guinea-Bissau, meanwhile, have now gone over seven Nations Cup games without a goal, last scoring in their second match of the 2017 finals when they made their tournament bow.
