The Japanese team showcased their class, creating numerous chances through sharp movement and precise passing, putting other tournament heavyweights on alert.
Three of Japan's goals were a result of well-coordinated upfield movements, marking the first time they scored more than twice in a World Cup game since their title-winning campaign in the 2011 tournament in Germany.
Midfielder Hinata Miyazawa opened the scoring for Japan midway through the first half, capitalising on an assist from Aoba Fujino to give the Nadeshiko a lead at halftime.
Mina Tanaka doubled Japan's advantage with a goal from Jun Endo's cross, providing some relief to the forward who had seen two earlier strikes ruled out due to offside decisions.
Tanaka then turned provider for Miyazawa's second goal, and Endo sealed the deal by firing home the fourth goal in front of a crowd of 16,111 in Hamilton.
In the final minute of stoppage time, substitute Riko Ueki was brought down by goalkeeper Catherine Musonda, resulting in a penalty for Japan.
Musonda received her second yellow card for the foul, leading to her substitution with Eunice Sakala, who made a spectacular save from the spot. However, Sakala's early movement resulted in a retake, and Ueki made no mistake with her second attempt, securing Japan's victory.
With this win, Japan moved to the top of Group C, ahead of Spain, who defeated Costa Rica 3-0 in Wellington on Friday.
Zambia's youthful side entered the tournament with high hopes after defeating Germany in their final warm-up game.
However, they struggled to create clear chances during the match, and their misery was compounded when key attacking midfielder Grace Chanda was ruled out of the tournament due to illness.
Despite the disappointing result, Zambia will be looking to regroup and showcase their potential in the remaining matches of the 32-team tournament.
As for Japan, their commanding performance has set the tone for their journey in the Women's World Cup, and they will be eager to continue their winning momentum in pursuit of another title.