Victory for Danny Lennon's side would all but guarantee their place in the Scottish Premier League next season.
While they are just three points ahead of bottom club Hamilton Accies, the Buddies' superior goal difference would have them avoid the drop into the Irn-Bru First Division if the sides finish on equal points at the end of the campaign.
Defeat for Saints and an Accies win against St Johnstone tonight would set up a nerve-shredding season finale on Saturday.
But, having seen their advantage steadily whittled down in recent weeks, the Paisley club are eager to finally condemn their Lanarkshire rivals to life in Scotland's second tier.
McGregor said: "In an ideal world, you want to put it to bed as soon as possible. But football doesn't always work like that.
"From a neutral's point of view, it is exciting because there is action at both ends of the table in the last few games and there is a lot to play for. But, for ourselves, we know the job we need to do. We will be treating it as a cup final. We all want to stay in the SPL and that is what we have got to make sure we do."
St Mirren appeared to have guaranteed their top-flight place just a few weeks ago as they opened up a 12-point gap at the foot of the table.
A win over Billy Reid's side in Paisley was thought to be the final nail in Accies' coffin, but after seeing their relegation rivals close to within touching distance, McGregor is targeting one final push as the Saints stumble over the line.
"At one point we were 12 points clear, but we can't dwell on that," he said. "If we take too many negatives from the last few games then that will hinder us in the future. We know what we need to do.
"There are a lot of guys who are playing for their careers and their livelihoods, so there is a big incentive there for the players and the club.
"But I am confident we will come through it as there are too many strong characters in our team not to achieve our goal of staying in the SPL."
It has been a frustrating few weeks for Buddies boss Danny Lennon as he has seen his side pass up a number of opportunities to secure their status.
They have taken just one point from their last five fixtures and Lennon, who could be without midfielder Jim Goodwin for the trip to Pittodrie, has urged his side to step up to the plate tonight.
"There is belief in the dressing room that we can do that," he said. "Hamilton are due huge credit for the way they have played in recent weeks.
"Ten points out of 12 is a terrific return. It is what Rangers have achieved and it is more than Celtic have achieved.
"We are only focused on winning tonight and, if each of our players play to their potential, then that is all I can ask.
"It is going to be a real test of our character, but we have players capable of getting a positive result."