That feat could be achieved if Scotland slip up against Samoa next Saturday and the Brave Blossoms overcome the United States the following day, though Japan coach Eddie Jones was in realistic mood.
"You look at the history at the World Cup between USA and Japan; USA have won every game," Jones told reporters on Sunday.
"In 2003 they played at Gosford north of Sydney. I remember my father went up there to watch it and Japan were favourites to win that game and they got beaten easily."
Japan began the tournament with a stunning 34-32 win over South Africa before being crushed 45-10 by Scotland and Jones said that preparations this week have to be spot-on.
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"It’s the same situation on Sunday. We’ve got to go out there and play our best rugby, play with physical and mental intensity," he said. "So it’s all got to do with how we prepare for the game."
Centre Male Sau and lock Hitoshi Ono sustained injuries against Samoa and winger Akihito Yamada suffered a blow to the head.
"Male and Hitoshi will get examinations tonight," Jones said. "Yamada is fine, he’s recovering really well. He just has to follow the concussion protocol."
Prop Keita Inagaki was pleased by the disciplined performance against Samoa in Milton Keynes.
"We did our homework on them and it all went according to plan," he said. "We didn't let them score for most of the game, so it's a shame we gave away that try."
"But it's over and done with. As (captain Michael) Leitch said in the dressing room, it's all in the past now and we need to turn our attention to the USA game."
A good day for Australian Jones was completed by the Wallabies knocking England out of the tournament.
"It was a good day to be Australian yesterday. Lucky enough to be coach of Japan and, with a nice glass of red wine, watched Australia beat England," he said.
(Reporting by Ed Osmond; Editing by David Goodman)
