Nasinu earlier defeated AOG in pool play 10-3 in a grueling encounter.
Despite the previous result, AOG coach Eroni Vereivalu said Nasinu scored a try in the pool game from their mistake.
Vereivalu added Nasinu may be one of the best teams in Fiji but they are confident of beating them.
In the finals this week, AOG will play Nasinu Secondary in the under 18 grade, Ratu Sukuna Memorial School and Marist Brothers High School in the under 17, while Suva Grammar and Marist will meet in the under 16, 15 and 14 grades.
Meanwhile, the losing semifinalists still have a chance to qualify for the Deans competition if they win the third place playoffs this week.
Suva Grammar and Marist Brothers High School will battle in the under 18, John Wesley College and Dudley High in the under 17, Laucala Bay Secondary and Ratu Sukuna Memorial School meet in the under 16, Dudley High faces John Wesley in the under 15 while Latter Day Saints meets Dudley high in the under 14.