The top six is set and the Centurions cannot finish any higher than fourth after a critical loss to Willetton last weekend.
Joondalup holds fourth spot by just a point over South Perth and two points over Subiaco.
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A win against Bayswater Morley at Hillcrest Lower Oval in round 15 this Saturday would guarantee the Centurions finish in the top four, while a loss could have them fall to sixth.
The top three cannot change with Claremont-Nedlands taking the minor premiership, Fremantle second and Perth third.
Should Joondalup finish fourth, the side would play Perth and likely get a second chance if it lost.
The highest-placed loser in the first round progresses to the preliminary finals along with the three winners.
The only way the Centurions would not get a second chance is if Claremont-Nedlands lost against sixth place or Fremantle lost against fifth, which is unlikely given the sides’ dominance this season.
Joondalup would face a daunting task if it finished below fourth and faced a must-win clash against the Tigers or Port Boys, having not beaten either side this season.
The Centurions blew their chance for a home final after falling 73 runs short of the Dragons’ 9-342 (dec) on day two at Iluka Sporting Complex last Saturday.
The hosts ended the match on 269 with half centuries from Clint Hinchliffe (59) and Garrick Morgan (56) the notable contributions.
Willetton’s D’Arcy Short (4-109) and Matthew Hanna (4-68) did the majority of the damage with the ball.