The Land of the Rising Sun drew first blood in the ninth minute when striker Motomi Kawamura emerged from a scrum, as new Kiwi goalkeeper Grace O'Hanlon couldn't prevent the prod from a scrambling defence despite lying across the goalmouth.
Regrettably for the parochial fans, it was Japan's Yu Asai who stunned them into silence with a 2-1 ice breaker from a penalty corner.
"We were a bit stand offish and a little bit shy and scared of the ball, I think, in the first half," said the 24-year-old Northland Olympian.
It was reminiscent of the Hockeyroos drawing 1-1 with Team USA in the 4pm start.
Brooke said while the Stacey Michelsen-skippered Kiwis stepped up in the second spell, they didn't put away the many chances they created.
"We have a lot to work on leading into [today's] game," she said of the 3pm match against the Hockeyroos.
Brooke said while Australia had a similar template of new blood, the Black Sticks desperately need to get on the same page and be more clinical in both circles.
While they had shown a sizeable improvement in the second warm-up match against Team USA, there were no excuses for last night's type of capitulation.
"We need to step it up [today] to show we've got what it takes to win this tournament," she said of the defending champions.
She agreed everyone were semifinalists in the tourney and their second outing would be a chance to make amends.
Asai was delighted with her goal, although she thought the high ball was going to be ruled a foul.
"We always kept faith in winning," said the beaming rookie defender through translator Taiga Yamaguchi, 18, of Napier.
It was only her second goal in a one-year international stint at the elite level.
Asai said the team's biggest concern during the hour-long flood delay was remaining mentally in the competition mode.
"Nothing like this has ever never happened before in my career," she said.
Japan coach Kenji Hasebe had impressed on his troops to be on their toes when play resumed because the Black Sticks were expected to run back on with all cylinders firing.
It is early days. Just as anything can happen in a match in the dying seconds all teams are capable of modifying their blueprints to mutate into a different beast before next Sunday's decisive second-round matches.
World No 6 Team USA, to say the least, look the most likely to lift the cup if the first round of competition is anything to go by.