The Young Nadeshiko are the only team thus far to have finished the group stage with maximum points, and while England could match this achievement later today, Japan's achievement was all the more impressive for the fact that it was secured with a virtual second string - and, for 72 minutes, with only ten players.
Japan's perfect record looked under threat in the early stages, however, especially when Jacqueline Gonzalez fired the already-eliminated Paraguayans in front from the penalty spot on 20 minutes, an incident which also led to Minori Chiba's dismissal.
The Asians have proved irresistible going forward, though, and even without star forwards Mana Iwabuchi and Chinatsu Kira, they were still able to strike three times in the space of seven minutes to head into the half-time break with a 3-1 lead.
Captain Natsui Kisikawa led by example, hauling the Japanese level, and Marika Ohshima and Haruka Hamada then added further goals before the Paraguayans knew what had hit them.
Hamada completed her double six minutes into the second half and although Gloria Villamayor reduced arrears three minutes later, Kishikawa made sure of victory 17 minutes from time before Saori Takahashi added a late brace to round off the scoring.