After enjoying their biggest ever World Cup win with an opening 7-0 romp against Costa Rica, Spain were unsurprisingly tested much more severely in their second game against Germany, with the final 1-1 scoreline probably a fair reflection of the game.
Spains' superior goal difference is almost as good as an extra point, and could prove crucial in the event that they lose to Japan and Germany beat Costa Rica.
Indeed, some cynics are suggesting that Spain might actually benefit more from losing this game and finishing second, an outcome that could see them avoid Brazil in the quarterfinals and/or Argentina in the semi finals (assuming both those teams win their groups), and also eliminate European rivals Germany for good measure.
However, that would involve an element of risk, because should Germany also beat Costa Rica by an improbable (but still possible) large enough margin to create the required swing in goal difference, then it could be Spain on the early flight home.
History suggests that it would be unusual if Spain were to lose, because they are unbeaten in their last nine final group games at World Cups, with 2018's 2-2 draw with Morocco ending a run of eight straight wins at this stage.
Japan, meanwhile, have already tasted both sides of shock results in their opening two games. They initially caused a seismic shock when coming from behind to stun Germany 2-1, only then to slide to a disappointing 1-0 defeat at the hands of the same Costa Rica side that had performed so woefully just four days earlier.
Victory over Spain will ensure Japan's progress, and they could even qualify with a draw if Costa Rica fail to beat Germany or if Germany only win by a one-goal margin. At the same time, defeat will see Japan eliminated, such is the knife-edge on which Group E rests.
Japan's coach Hajime Moriyasu faces selection problems, as defenders Takehiro Tomiyasu andi Hiroki Sakai are both injury doubts, while midfielder Wataru Endo is also likely to be sidelined with a knee injury.
In the Roja corner, recent media news suggests that head coach Luis Enrique plans to return to club management after this World Cup, and if that is the case he will be looking to leave the international stage in style.
Enrique might be without the services of young midfielder Gavi, who recently missed training because of a minor injury, while captain Sergio Busquets is only one yellow card away from being suspended and might be rested to save him for the knockout rounds.
Alvaro Morata continued his impressive record at international level, coming off the bench to score in both of Spain's games, and he is now favourite to start in Spain's attack, where he will fancy his chances of adding to his tally.