The Australian Gems have dropped their opening game of the FIBA Under-19 World Cup against an impressive defensive display from Japan.

The Gems never truly found a rhythm in the game despite the best efforts of Ezi Magbegor with their back court scoring just nine points in a 61-66 defeat.

Magbegor was a bright spot in the loss, recording 21 points, five rebounds, two assists, three steals and three blocks and a dominant third term looked like it may be enough to carry Australia to the victory.

Japan's hard-nosed defence kept them in the game though and a +9 advantage from beyond the arc also proved critical as the Gems shot 1-20 on three-pointers and 35% from the field overall.

While not as small as some international Japanese teams, Australia still looked to their advantage inside early through Chloe Bibby and Magbegor.

Their front court starters scored the first six points for the Gems and foul trouble for Japan's Stephanie Maluwi then opened up more opportunities around the basket for the Aussies.

Japan were not giving up any easy looks though, holding Australia to just 24% shooting in the opening term with the game tied at the first break.

The Gems continued to move the ball inside in the second period and finally saw some dividends with Anneli Maley (four points, 13 rebounds-seven offensive) helping put together a 10-5 run.

Japan drilled an answering three-pointer to claw back though and a buzzer-beater on half-time then gave them a three-point edge with all 28 points for Australia originating from their front court in what was becoming a predictable offence.

Rocci was the first Gems guard to hit the scoreboard and she did so early in the third term while Magbegor and Bibby (ten points, seven rebounds) continued to knock down shots as well and Australia quickly regained their advantage out of the main break.

Mawuli was then called for her fourth foul as Japan's interior defensive issues worsened with Magbegor taking control of the game at both ends of the floor.

She forced the opposition into countless fouls while racking up steals and blocks at the defensive end to give Australia a five-point edge midway through the third quarter.

However, Japan came back with another three-pointer as the long-range game continued to haunt the Aussies, cutting their lead to just four at the final change.

A fourth trey kicked off a 9-0 run for Japan to move them in front and they never looked back.

A Samantha Simons (seven points, two steals) banked three-pointer finally broke the long-range drought for the Gems and reduced the match to a one-possession game inside the final 30 seconds.

They then got a stop at the defensive end and had a chance to send the game into overtime but Simons could not repeat her heroics and Japan sealed the win from the free-throw line.

Find all the stats from the game here.

In addition to their disappointing shooting display, Australia will also be keen to atone for their 24 turnovers (which matched their 24 field goals) when they next hit the court tomorrow night.

Watch a replay of the game vs. Japan below.

The Gems will now take on Mexico late Sunday night/early Monday morning AEST at 12.15am on July 24 and you can watch that game live via FIBA's YouTube channel here.

Australia's Schedule for the Under-19 Women's World Championships (all times AEST):
July 24: Australia vs. Mexico at 12.15am
July 25: Australia vs. Hungary 10.00pm
July 26: Round of 16
July 28: Quarter-Finals
July 29: Semi-Finals
July 30: Bronze and Gold medal games