Dodgers, the defending champion, qualified for the season-ending championship by beating Saints 8-5 in the major semifinal at Ellis Park.
It will be a Dodgers-Cardinals clash in the best-of-three finals to be played this Saturday.
Saints had to settle for third, with Ellis Park finishing fourth and Waverley fifth.
Dodgers' win in the late 2 v 3 game was set up by teenagers Ben and Cam Watts.
Ben slugged a home run in the first inning and then bashed a grand-slam homer in the second to set the game alight, and Cam cleared the fence in the sixth inning.
Earlier, Dodgers had held on to beat Saints 9-8 in one of the last two games of the regular season.
Saints had built a nice 5-1 lead through five innings and was getting excellent work out of pitcher Sam Jones, who had retired 14 of 18 batters faced and had an incredible 10 strikeouts.
But Jones ran out of gas in the sixth, Saints committed three errors, and Dodgers piled on five runs.
With three more at the top of the seventh, Dodgers went up 9-6.
Saints picked up two runs, on a ground-out and a wild pitch, but fell just short.
Top qualifier Cardinals suffered an upset - although not one that had any bearing on the standings - when it was beaten 5-4 by Ellis Park.
Ellis Park was up 4-1 through three innings, with veteran pitcher Pete Mathieson keeping the Cardinals bats quiet.
Both teams scored on sacrifice flies in the fourth but offence was in short supply as both Mathieson and Cardinals hurler Shane Whaanga kept it tight.
Crete Whaanga got Cardinals within two with a solo homer in the sixth, and the gap was closed to one when Mark Ludlow scored on a wild pitch in the seventh.
