Ross Perry made his long awaited comeback into the side with Steven Forbes moving forward into midfield in place of Thomas Kindbendiksen and young Chris Craig got a rare start replacing Giorgis Efrem out on the left wing.
It was an opportunity for Craig to show what his is capable of from the start, instead of his normal substitute role, and the youngster grabbed it with both hands in an outstanding opening 45 minutes.
After only 18 minutes the winger played a defence splitting pass to Isa Bagci who had found space between two opposition defenders on the edge of the 18 yard box and calmly drew out Darren Stewart before slotting the ball past the Paisley stopper to open the scoring.
Craig then set up Ross Perry with a delightful cross from a corner kick but the lack of match practise showed as the big defender's header missed the gaping goal completely.
Chris Craig then had an opportunity to get a well deserved goal for himself on 35 minutes but his well struck free kick was superbly touched round the post by Stewart as the ball headed for the top corner.
From the resultant corner Jamie Ness attempted an audacious overhead kick which was net bound until a black and white shirt appeared on the goal line to clear the danger.
Half Time - Rangers 1 St. Mirren 0
It only took five minutes of the second half for the Light Blues to double their lead when Forbes released substitute Andy Little, who had replaced Ross Perry at the interval, down the right and his low cross was met perfectly by John Fleck who slid in to score from 8 yards.
Two minutes later saw the Buddies get right back into the match when Steven Forbes attempted to clear a dangerous cross from the left but the right back only succeeded in slicing his clearance past the bewildered Gallacher into his own net.
This gave the visitors a massive boost and a minute later the Paisley side almost levelled thanks to great link up play between Jon McShane and Andy Stirling with the former setting up the latter with a pass which split the home defence and left Gallacher to narrow the angle enough for the shot to go wide by the narrowest of margins.
The match had now exploded into life as the young Buddies sensed a great chance to leave Murray Park with a point, with the Light Blues determined not to slacken their grip on the title the crowd were enthralled as both side went all out attack.
Paul Quinn, who scored the Buddies match winning goal in their victory over Celtic, picked up on some slack defending and was only denied by a brilliant tackle from the brave Gallacher.
Isa Bagci then saw himself in a similar situation moments later and again it was a keeper who came out on top as Stewart blocked the big Swede's shot with his body.
Steven Kinniburgh then tried his luck with a powerful shot from well outside the box but his effort smashed off the bar and following a goal mouth scramble Bagci shot over.
Paul Quinn was proving a massive threat for the visitors and again had a terrific opportunity towards the end of the match as he burst into the box but saw his first shot well blocked by Ross Harvey and then the rebound blocked by the outstanding Gallacher.
There was no shortage of commitment from both sides and referee Colin Steven had to show the yellow card to Gaffney and Quinn of St. Mirren and Forbes of Rangers as the match entered the closing stages.
The Teams;
Rangers - Gallacher, Perry (Little 45), Kinniburgh, Wilson, Harvey, Ness, Forbes, Shinnie, Bagci, Fleck, Craig (Mitchetslaeger 82).
Subs not used - Vaiculis, Durie, Donald, Campbell, Van Den Broeck.
St. Mirren - Stewart, Rawcliffe, Love, Gaffney, McMechan, Crighton, Stirling, Carson, McShane, Quinn, Murray
Subs - Faulds, McCabe, Cunningham, Gair, Quirk
Referee - Colin Steven