- Hikaru Naomoto (25')
- Aoba Fujino (27')
The Nadeshiko reprised the effervescent passing game of their opening 5-0 win over Zambia and will progress to the round of 16 for the fourth straight World Cup if Spain, as expected, beat the African side in Wednesday's later Group C game in Auckland.
"We did what we needed to do, and we did it well," Japan coach Futoshi Ikeda said.
"We've prioritised winning points. The players came here with a serious goal in mind and we're all looking towards that same goal."
Playing through Mina Tanaka in an advanced midfield role rather than playmaker Yui Hasegawa as they had against Zambia, Japan were already well in the ascendant before the double blow that knocked the stuffing out of the Central Americans.
Left winger Hikaru Naomoto struck first in the 25th minute, pouncing on a slip from Maria Paula Coto and storming into the area before stroking the ball into the net past the dive of goalkeeper Daniela Solera.
Two minutes later, teenager Aoba Fujino turned a defender on the right wing, ran directly at goal and beat Solera at her near post from a tight angle.
Costa Rica, who were beaten 3-0 by Spain in their opener, were barely able to land a blow on their opponents and it looked from then on only a matter of how many goals Japan would rack up.
Despite having 25 attempts on goal, however, Japan were unable to add to their tally - a shortcoming that might concern Ikeda with tougher challenges lying ahead.
Japan face Spain in Wellington on Monday in a match that will almost certainly decide which of the two sides top the group, while Costa Rica - still seeking their first World Cup win- will take on Zambia in Hamilton at the same time.
Costa Rica coach Amelia Valverde, who blamed lapses of concentration for the two goals, was asked whether it was time to bring an end to her eight-year reign.
"I'm totally focused on having the best World Cup possible in the circumstances," she told reporters.
"We still have a match to play and, for us, all matches are important. I don't think this is the right time to talk about that."
- Maria Ferrieri Caputi