Facing the most effective offensive team across the competition in Japan, Australia knew they had to be at their best defensively and Ashlee Hannan set the tone from the start with a big rejection.
Japan learned their lesson quickly though and began peppering the scoreboard from outside, jumping out to a 15-7 lead while starting 3-3 from the three-point line.
At the other end of the floor, the Sapphires struggled to find the bottom of the basket but their hustle on the offensive glass via the likes of Alex Fowler (seven points, ten rebounds, two blocks) ensured the margin stayed manageable as they pulled down eight offensive boards by quarter-time.
The speed of Shyla Heal and the precision of Isabel Palmer ensured they broke through any Japanese full court press with ease as well and at the first break, the Aussies trailed by eight.
Japan did not cool off in the second period, pushing the deficit beyond double-digits despite Last-Tear Poa (seven points, seven rebounds) drilling her team's first three-pointer of the game.
Heal then provided the real spark for the Sapphires, knocking down a huge long-range basket to beat the shot clock while on the next possession, they held Japan to a shot clock violation.
Still trailing by nine at half-time, Australia had stepped up their defensive intensity and Japan were held to just two points over a ten minute stretch across the second and third terms.
Out of half-time, Palmer (14 points, four assists) scored a quick five points and the Sapphires' swarming defence forced Japan to take outside jumpers on almost every possession.
Defying foul trouble, Agnes Emma-Nnopu asserted herself in the paint as well to help Australia draw level momentarily before a late triple kept Japan's noses in front heading into the final stanza.
The Sapphires were on a mission though and when Georgia Amoore (ten points) connected from the corner, she gave Australia their first lead.
Emma-Nnopu (ten points, ten rebounds, three blocks) then showed her skills in the open court with a spin move and lay-up while Heal (nine points, six rebounds) got a nice scoop shot to go as the Sapphires went on a 9-0 run to take control.
Japan were not done with though, nailing a three to make it a one-point game inside the final 43 seconds and they had a chance to move back in front on the next play but the shot just rimmed out.
Time then proved their enemy and they were not able to foul quickly enough to stop the clock as the Sapphires clinched a memorable victory.
Watch the replay of the game below and find the box score here.
In addition to the Under-16 Asian Championship gold medal, the Sapphires also qualified for the 2018 Under-17 World Cup earlier this week where they will be aiming to defend their title from two years ago.