The final place will go to either Bristol Central or Team Northumbria, who have their final Division 1 matches tomorrow (Sunday).
Invicta went behind on three occasions against Northumbria but, from 9-9 at the start of the final quarter, they surged ahead with vital goals by Ben Carter, Jack Waller and Conrad Rhodes.
Manchester again left it very late to complete an 8-7 win against Bristol. They were not ahead for the first time until Guile Shafie made it 7-6 with the last minute buzzer about to sound. Ashley Castle then equalised but, with 33 seconds remaining, Eleftherios Chelioudalis struck the winner for Manchester.