Manly finished the regular season on top of the Shute Shield ladder, but it's Warringah who will take the favourites tag into the final Battle of the Beaches.
The Rats cruised to victory over Randwick in week one of the finals, where the Marlins went down in their opening post-season clash.
“We certainly didn’t expect the score line in last week’s match, most aspects of our game were pretty strong," Rats coach Darren Coleman said.
"We’re not reading too much into Manly’s form, they beat us last time at home when we were in good form, so the derbies are always tight and competitive."
Manly coach Brian Melrose said his side had been handed a wakeup call in that first clash.
“The essence of why you play the game is to be able to put yourself at the point where it’s as dark as you can get and see how you react," he said.
"We didn’t respect the advantages we had, but we deserved the chance of a second bite, and we’re going to put our best foot forward.
"Every player has a choice, he can choose to turn up and make a difference, or he can choose to turn up and hope."
Warringah vs Manly, Pittwater Park, 3:10pm AEST, LIVE on 7TWO
Rory O’Connor, Rob Kelly, Sam Needs, Jack Tomkins, Cam Treloar, Maclean Jones, Tom Connor, Sam Ward, Josh Holmes, Myles Dorrian, Harry Jones, Josh Gillard, Seb Wileman, Sailosi Tagicakibau, Dave Feltscheer.
Sio Tatola/Mitch Lewis, James Hilterbrand, Gunnz Fuavao, Ryan Melrose/Ed Gower, Adrian Hall, Sam Shires, Kotoni Ale, Dan Alley, Tim Donlan, Sam Lane, Tom Chesters, Kevin Fuavao/Nick Holton, Dennis Pili-Gaitau, Cam Brailey, Josh Turner
Norths vs Eastwood
Defending champions Norths also managed a shock win last weekend, defeating Souths at Forshaw Park and winning the right to host a home semi-final.
Norths coach Simon Cron, who will be heading to the Waratahs at the end of the seasons, said only perfection would help them through to the big dance.
“Our transition speed was good last week, but our attack was poor, so we’ve been working on our execution there," he said
"We need to get a lot better this week, they’ve got great players across the park, and the boys must be ready to perform and play likely 85 minutes of knockout rugby. We have to nail every facet of our game."
Though they shocked the competition in week one Eastwood coach Stu Woodhouse said they couldn't rest on their laurels.
“We need to be better this week against the Shoremen, particularly our attack and some of our defensive reads," he said.
"We need to move on quickly from last week and refocus, build on the Manly result. We need to take every opportunity we get, because they will not offer as many."
Norths vs Eastwood, North Sydney Oval, Sunday August 20, 3pm AEST LIVE on 7TWO
Ezra Luxton, Sam Kitchen, Lawrence Hunting, Hugh Sinclair, Conor Vest, Gary Bautz, Will Miller, Michael Wells, Nick Duffy, Angus Sinclair, Lachlan Creagh, Harry Burey, Cameron Clark, Richard Woolf, Augustin Slowik.
Jed Gillespie, Hugh Roach, Rob Lagudi, James Neale, Lachie Cannell, Michael Kovacic, Tevita Piukala, George Kent, Matt Gonzalez, Blake Sutton, Zack Mackay, Tom Hill, Mike McDougall, Fabian Goodall, Liam Windon