Rika Masuya was on target twice in the opening 17 minutes, Yui Narumiya grabbed a brace of her own in the second half, and Hina Sugita was also on the scoresheet in between times.
The Asians overwhelmed their South American counterparts from the first whistle and were ahead within two minutes, Masuya converting a simple rebound after Yui Hasegawa’s shot struck the crossbar.
Taking advantage of their opponents’ sudden insecurity, Japan pressed forward and hit the woodwork again after 14 minutes. Ayaka Inoue made space for herself on the right and her effort came back off the bar.
Two minutes later, however, the Japanese got their second. Hasegawa was again the creator for Masuya with a perfect through ball, which the latter finished off nicely.
Sugita made it four just after the hour mark, beating a defender before giving Nicole no chance, before Narumiya rounded off the scoring with a sensational individual effort.
The No9 dribbled past several defenders and struck a shot which hit the crossbar but landed back at her feet for a sumptuous finish, the icing on a perfect Japanese cake.
Hiroshi Yoshida’s side continue their campaign on Wednesday against New Zealand, while Brazil face Mexico earlier on the same day.
"I didn't expect this kind of victory at all, because always the first match of a tournament is very difficult. I think that it was thanks to that lucky goal at the beginning that made it easier to beat Brazil." Hiroshi Yoshida, coach of Japan