The Crusaders have swept aside the Melbourne Rebels 52-26 in Sydney, but need the Blues to slip up against the Western Force to qualify for next weekend's final against the Highlanders.
Needing a 33 point margin of victory to guarantee another week in the competition, the Crusaders threatened to overrun the Rebels, but couldn't quite match that mark.
Scott Robertson's side were as much as 26 in front, including for the final 10 minutes and thought they had done enough when centre Leicester Fainga'anuku crashed over.
But the bulking back was ruled to have completed an extra movement on the ground and was penalised.
A final attack was thwarted by the Rebels and the Crusaders are now forced to watch with interset as the Blues host the Force.
Two second-half tries to Sevu Reece, who scored a hat-trick on the day, Ollie Jager and Braydon Ennor not enough to for the Crusaders to host the final - the best they can hope for is a trip to Dunedin to take on the Highlanders in a Southern derby, Super Rugby Trans-Tasman final.
The plucky Rebels doing just enough to ensure the Highlanders play a part in the final next Saturday night, regardless of the final result in Auckland.
The Crusaders started with a bang, scoring two converted tries inside five minutes through Mitchell Drummond and Will Jordan.
Drummond scored after several phases close to the Rebels line, and what was to follow from the Jordan was something special.
Richie Mo'unga split open the defence from the restart before finding his fullback on the inside who skinned his counterpart George Worth and run away to score a scintillating try.
But the Rebels struck soon after - as they continued to do throughout the afternoon, through a 16th minute Trevo Hosea try.
Leicester Fainga'anuku and Sevu Reece scored back-to-back to lift the Crusaders to a 26-7 lead, but a 26th minute Jordan yellow card gave the Rebels a window.
Halfback Joe Powell pounced just before halftime to reduce the red and blacks' lead to 14 at the break.
Crusaders 52 (Drummond, Jordan, Fainga'anuku, 3 Reece, Ennor, Jager tries; Mo'unga 6 conversions)
Rebels 26 (Hosea, Powell, Vaihu, Lomani tries; Gordon 3 conversions) HT 26-12