Prosecutors ain't going down in their case against Robert Kraft without a fight ... they just filed docs saying a judge was wrong to bar them from using the graphic sex spa video in court.
78-year-old Kraft scored a huge victory in the case last May, when a judge ruled police surveillance video of him allegedly receiving sex acts inside the Orchids of Asia spa in Florida could NOT be used in the case.
The judge claimed when cops executed their search warrant and planted cameras inside the spa ... they didn't do enough to protect people who were inside the spa getting perfectly legal massages.
In court docs filed this week ... prosecutors are firing back at that ruling, saying the judge was DEAD WRONG -- and want the video to be allowed in the case against Kraft.
In the docs, they argue cops handled everything the right way in the investigation ... saying if police had taken bigger steps to protect potentially innocent people, it would have "frustrated the objectives of the search."
They claim that of the 39 massage recordings ... only 4 didn't capture illegal activity.
Prosecutors are asking the court reverse the suppression order ... and if it's granted -- it would mean the Kraft video has a chance to go public once again.
It's unclear when the Courts of Appeal is expected to make a ruling ... but it could be soon.