After the Sydney Roosters' defeat to Parramatta blew the race for eighth spot open, the Tigers looked ready to stay in the hunt on Sunday when they led 28-16 with 15 minutes remaining.
A win would've moved the three-time reigning wooden spooners only two points behind eighth, daring to dream.
Mid-season recruit Taylan May had nabbed two tries to help erase a 10-0 first-half deficit, before Jarome Luai celebrated his 150th NRL game with a first Tigers four-pointer that had the home fans ballistic.
But with his side seemingly down for the count, fullback Scott Drinkwater orchestrated a skirmish that yielded three tries in five minutes for a Cowboys side with nothing to play for - as far as finals were concerned.
The heartbroken Tigers' own finals hopes are now hinging on a miracle, given their for-and-against is significantly worse than the other three teams vying for the last remaining top-eight spot.
"I feel for everyone," said coach Marshall.
"The hope, and the hype and the results last night giving everyone a bit of hope into where we could end up. It's all been taken away after tonight.
"We're all feeling how our fans are feeling. Deflated, disappointed. Essentially, we had the game in our hands there and we let it slip through some comfortable actions that weren't good enough."
The only way the Tigers can secure a first finals spot since 2011 is to win their next two games and hope the Roosters lose of both theirs.
The margins of those four results will need to be more than 46 points on average, and the Tigers are also relying on the Dolphins and Manly's games falling their way.
Making matters worse, the Tigers look set to be without their form player Adam Doueihi for next week's already difficult clash against Canberra at GIO Stadium.
The halfback left Leichhardt Oval in an ambulance with suspected facial fractures after colliding with the knee of Cowboys veteran Jason Taumalolo early in the first half.
"He's still there (in hospital), getting sorted out. I'm guessing it's probably the end of his season," Marshall said.
The Tigers' quest for late points was rocked when Latu Fainu, Doueihi's replacement at No.7, left the field for a HIA in the final 15 minutes.
North Queensland looked ready to fold when Luai and Brent Naden scored in back-to-back sets for the Tigers with around 20 minutes to play.
But Semi Valemei, after a tough day defensively, crossed in the right corner to give the Cowboys a sniff, before Drinkwater's cutout pass to Braidon Burns helped them draw level.
Working upfield again, Drinkwater belted past Naden and had Jaxon Purdue in support, with the wiry youngster restoring the visitors' lead.
"I'm happy for the lads. It's a good feeling in there (the dressing sheds) at the moment," said Cowboys coach Todd Payten.
The Tigers had one final raid in the dying minutes but Jahream Bula's offload landed in the hands of Cowboys forward Reuben Cotter and the visitors held on.
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