The win also advances them to the gold medal game at this tournament where they will take on New Zealand for the second time in three days.
Australia were a little sluggish early against Papua New Guinea and trailed 4-8 midway through the first quarter.
However, they soon were able to put the disappointment of a two-point loss to New Zealand last night behind them.
They scored the next 25 points in a row leading into quarter-time and that gave them a buffer which they would never relinquish, going on to win every term convincingly including a 62-10 second half.
James Ingham led the way with 21 points and four steals but there were contributors all over the floor with Harry Johnson (20 points, four steals), Matthew Thomson (19 points, nine rebounds), Harrison Penisi (19 points, three steals) and a combined 26 points off the bench from Sejr Deans and Michael Walker.
Find the box score here and watch a replay below.
The boys now face a re-match against New Zealand tomorrow night at 8pm AEDT in the gold medal game for the tournament.
The girls have enjoyed a day off today after sweeping their group stage but they will also meet New Zealand in their gold medal playoff tomorrow, at 6pm AEDT.
The 2018 Boys and Girls Schedules for the FIBA Under-15 Oceania Championships (all times AEDT):
December 4: Australian Girls def. Samoa (111-29)
December 4: Australian Boys def. Samoa (90-49)
December 5: Australian Boys def. Fiji (119-27)
December 5: Australian Girls def. New Zealand (94-34)
December 5: Australian Boys def. Guam (113-30)
December 6: Australian Girls def. Fiji (141-15)
December 6: Australian Boys def. by New Zealand (57-59)
December 6: Australian Girls def. Papua New Guinea (155-18)
December 7: Australian Boys def. Papua New Guinea (121-31)
December 8: Australian Girls Gold Medal Game vs. New Zealand at 6pm (Live-Streamed)
December 8: Australian Boys Gold Medal Game vs. New Zealand at 8pm (Live-Streamed)