Japan are eager to take their performance up a notch against Costa Rica on Wednesday and build on their flying start to the Women's World Cup.

They hit the ground running with an impressive 5-0 thrashing of Zambia in Hamilton and want another barn-storming display in Dunedin against the Costa Ricans, who lost their opening game 3-0 to Spain.

Forward Mina Tanaka said the Japanese team was more relaxed after the win but called for them to raise their game and secure another three points to stay on course for the knock-out stages from Group C.

"Compared to the first match, we're less nervous," Tanaka told reporters Tuesday. "I think we could play better."

The Japanese want more rock-solid defending, having stopped Zambia from getting a single shot on target, but Tanaka said it wasn't as easy as it looked.

"The first match was tough. We still got five goals. They got zero shots. We did it as a team and that is wonderful," she said.

The 29-year-old was relieved to get her first goal of the tournament having had two earlier efforts ruled offside, and keen to cause the Costa Ricans a few more problems.

"I'm glad we got the (three) points, but I want to be more relaxed and contribute more to the team," she added.

Japan head coach Futoshi Ikeda hinted he may rotate the side ahead of their final group match against Spain next Monday in Wellington.

He said his team has grown in confidence, agreeing with Tanaka that there was more to come, but warned against complacency.

"I think we are getting used to the World Cup," he said. "I think we could bring out more too, but we don't want to be too complacent. We don't want to let them hit us when we are not looking."

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