Nigeria's group opponents at the Rio Olympics men's football event Japan won their first game at the 2016 Toulon Tournament in France after defeating Guinea 2-1 in a Group B clash on Wednesday.
Japan had lost 2-1 to Paraguay in their first game before going down 1-0 to Portugal in their second game.
Cayman Togashi gave Japan the lead when he scored as early as the third minute.
Guinea drew level in the 11th minute through Bangaly Soumah.
With six minutes remaining in the first half, Japan went in front again, thanks to Takumi Minamino.
Their next game comes up on Friday against England.
Japan are in Group B alongside Nigeria, Sweden and Colombia at the Rio Olympic Games.