The two powerhouses met at Mathoura, with Rochester only needing to halve one rink to finish on top.
Instead, the home side pulled out a performance from the top drawer to clean sweep the three rinks for a 16-75 to 0-33 result.
Mark Quor defeated Brian Trengove 29-8, Peter Holzer recorded a 29-10 victory over Diane Milgate and Christine Taylor edged out Richard Feuk 17-15.
The 84-shot turnaround on the ladder saw Mathoura finish level with Rochester on 134 points, but claim top spot courtesy of superior percentage.
It also meant Moama finished the regular season in third spot, just one point adrift.
The Steamers defeated Echuca 14-74 to 2-45 with Cameron Keenan and Wayne Stephenson the winning skips.
Echuca’s Roma Opie didn’t know it at the time but a 24-20 defeat of Olivia Cartwright ultimately proved the difference between Moama finishing top and third, and Echuca snatching fourth spot from Rich River, who lost against Deniliquin 14-59 to 2-53.
Pam Hayes was Rich River’s lone winning skip, a 27-18 victor over Linda Harris, while Craig Hillier and Conway Bovell got the job done for Deniliquin.
The semi-finals will feature return bouts between Echuca and Moama in the first semi-final and Mathoura and Rochester in the second semi-final.
Both matches will be at Echuca Bowls Club.
Division two saw wins to Mathoura, Rich River, Echuca and Moama.
The Steamers took the minor premiership courtesy of superior percentage with a 16-75 to 0-42 defeat of Ky Valley View.
Echuca defeated Tongala 15-69 to 1-36, while Mathoura 16-76 proved too strong for Rochester and Rich River upset Deniliquin RSL 12-56 to 4-55.
The opening week of finals pits Moama against Echuca in the second semi-final and Mathoura against Deniliquin RSL in the first semi-final.
Winners in division three were Moama, Deniliquin, Lockington and Elmore.
The Steamers’ 14-48 to 0-23 defeat of Echuca resulted in Moama claiming the minor premiership from its cross-river rival.
Kevin Connolly defeated Bernadette Johns 28-11 and Peggy Bell recorded a 20-12 defeat of Jillian Young.
The two clubs will meet in the grand final qualifier at Rich River, while Elmore and Deniliquin will take winning form into the first semi-final, where defeat will spell the end of the season for the loser.