In yesterday's game, New Zealand managed 25 circle penetrations to Argentina's 15, and squandered three open nets. Two one-on-ones with the Argentine goalkeeper went begging.
By contrast, Argentina's three goals came from just six shots.
"We have to tighten up a bit because the good teams will punish you," Hager said.
He is hopeful attacker Sophie Cocks will play a part in the friendly against Germany tomorrow night (NZT) to prove her fitness after suffering a blow on a leg against the United States recently. She played a small part in both games against Argentina.
Key defender Liz Thompson also picked up a bang on a leg in yesterday's game.
The Black Sticks' opening cup game is against world No10 Japan on Sunday morning (NZT).