Corrimal sensed an opportunity to snare a breakthrough victory, but a second-half sin-binning and a desperate Collegians conspired to deny them at Ziems Park.
The Cougars are anchored to the bottom of the ladder and have already parted ways with coach Trevor Schodel this season.
But the return of inspirational leader Jacob Hind from his Country campaign in Hawaii spurred them to the brink of a win.
However, they failed to find the game-winning play, falling 26-24.
The win has guaranteed Collegians' ticket to the finals but they have a steep curve ahead to defend their crown and beat front runners Helensburgh and Thirroul.
In a thrilling contest, Corrimal scored a late try after hooker Kris Walton was sent for a 10-minute break for repeated ruck infringements.
Walton, along with Hind, had been Corrimal's best to that point, as Collies dropped enough ball to ensure their rivals remained within sight of victory.
Controlling much of the first half, the Cougars were rewarded with a 12-6 lead before an intercept try allowed Collies to level the scores.
Collies then clawed their way to a 26-18 advantage, a string of penalties adding to Corrimal's frustration, before Walton was sin-binned.
The Cougars came charging back in the final 15 minutes, scoring a try to reduce the margin back to two points.
The Cougars face a difficult assignment against Nathan Fien's in-form Thirroul outfit this Saturday, before taking on fellow stragglers Dapto in the final round.
Dapto, now denied any hope of finals action as a result of Collegians' win, meet the reigning premiers on Friday night, while Helensburgh host Wests on Sunday.