The proverbial six pointer, Saints win it and they shoot up the table to 12th and 5 points clear of the frop zone, but if they lose it then it is a big worry.
Saints have to go out and show the fight they showed at Old Trafford, however as great a result as it was in the home of the devil himself, we have to also recognise that it was not a perfect performance and could so easily have turned into a glorious defeat as it did at Stamford Bridge, lapses in concentration could have cost us dearly on Saturday, we have to make sure that they do not happen again tonight.
This is a big game for the manager, the fans have been calling for his head of late, but the board have kept quiet and rightly so, we do not want to go down the line of panic everytime something is not going well, Pellegrino has to be given time to show that he is or isn't the man to take us foward.
Having said that if we fail to win tonight that will make it 9 games without a win and indeed only 2 wins in 17 games since we beat the Eagles up at Selhurst Park back in September, to be blunt this is not acceptable, Mauricio Pellegrino has to get his show on the road and fast, if he were to fail to win tonight then it is hard to see that he can continue going forward, indeed even if he was to win it would still leave many question marks over his management, it would perhaps only paper over the cracks.
Sadly Pellegrino has made too many errors in recent months and they are all coming home to roost now with injuries and suspensions etc working against him, there is a big gap between today's game and the next Premier League fixture at Watford, plenty of time to make change if deemed necessary.
But Saints stil have the team to win this one, it just needs the manager to be able to put out the right side, to recognise the players that are doing well and keep them in the side.
At the back there is not much to choose, Alex McCarthy will surely keep his place and in the back line he does not have much option for change, the only question will be if Ryan Bertrand is fit to return, if he is with respect to both Matt Targett and Sam McQueen who have both deputised well in his absence, then he has to play.
In midfield it is more difficult, both Hojbjerg and Romeu were outstanding at Old Trafford, they have to stay in, but does he keep in JWP to hold the ball and pass it or does he bring back Mario Lemina.
Dusan Tadic and Sofiane Boufal likwise deserve to stay in the team, however i have a feeling that one might be rested and Nathan Redmond come back in, if only to negate the pace down the flanks that Palace have.
Up front it is difficult, Shane Long did superbly against United as the lone striker, he is better suited to this role than Manolo Gabbiadini, so I would expect him to keep his place, although as we now know "expect" is not a word that you can associate with Pellegrino's team selections.
So again the key could well be who is on the bench and can they change the game, sadly our attacking options are limited and that could be a problem.
This is a must win game, as i keep saying we are not a bad side, indeed if we had just held on against Arsenal and Huddersfield in our last two home games instead of gifting them soft goals then we would now be 11th and looking at a win tonight to push us up to 9th.
Of course that is all ifs and buts, but that tells us the story of the season, we are not far off where we want to be and that is in the top 10, we have been the architects of our own downfall too many times this season, too many goals have been down to poor marking and we can't keep doing that, at Manchester united we got away with it, as we found against Burnley, Arsenal & Huddersfield in our last three out of our last four home games we cannot keep giving people free headers and expect to keep clean sheets.
So tonight has to be about positivity, from the manager, from the players and just as importantly from the supporters, this has to be one of those games that turns a season and turns it in the right direction.