Defeat away to Glasgow last time out looked to have put the nail in the coffin for the Ospreys but with British Lions Adam Jones, Alun Wyn Jones and Justin Tipuric all starting, there remains more than enough quality for the Ospreys to secure an away win.
"All the hard work of the last nine months rests on Friday evening," said Tandy as he looked ahead to tonight's game.
"I was extremely disappointed with our performance up in Glasgow last time out. We didn't do ourselves justice and that defeat has opened the door for the Scarlets, allowing them to jump ahead of us with one game to go.
"We know we're up against it if we are going to reach the play-offs but we definitely won't be throwing the towel in. This team isn't about that, it's about playing for the cause and giving everything. The boys were hurting badly in the dressing room in Glasgow and are desperate to not go out with a whimper.
"We still have a chance of progressing so Friday night will be about giving it everything. If we can put in the kind of performance that's needed then we'll have to wait and see what happens elsewhere."
With the Ospreys now forced to rely on other results going in their favour, Tandy admits his side's slow start to the season may have cost them.
And to make matters worse, he is without Lions hooker Richard Hibbard and scrum half Kahn Fotuali'i. British Lions Jonny Sexton, Rob Kearney and Sean O'Brien all start for second placed Leinster while Brian O'Driscoll is on the bench.
"Just to get into the play-offs is extremely difficult. We gave ourselves an awful lot to do after losing the first three, particularly with home defeats to Glasgow and Ulster," Tandy added.
"But now we just have to give it everything on Friday. The PRO12 is an extremely tough competition, we're up against back to back European champions and this year's Amlin finalists on Friday night.
"There'd be nothing worse than giving up the fight and then getting back into the changing room after the game on Friday to discover Treviso had done their part in Llanelli. As long as the maths mean we still have a chance we'll be going for it. It's going to be an interesting evening."