This was however a far-from-impressive performance from the SPL Champions, who struggled for long spells of tonight's game after taking an early lead.
Rangers Manager Walter Smith made two changes from Saturday with Nacho Novo and Kenny Miller both making welcome returns from injury to replace Kevin Thomson and John Fleck.
The Ibrox men got off to the perfect start, opening the scoring inside two minutes when Steve Davis beat the offside trap to latch onto a Kyle Lafferty chip and stroke the ball home.
Lee McCulloch almost made it two in seventeen minutes when his shot on the turn came back off the underside of the bar.
Five minutes later a Davis shot from a Steven Whittaker cross was blocked, then immediately afterwards McCulloch, breaking upfield, saw his effort held by home goalkeeper Paul Gallagher.
It had been all Rangers in these opening stages - but as the half wore on Saints came more and more into the game.
The half however ended with just that early goal between the teams.
Steven Whittaker came close to adding a second in 48 minutes when his low twenty-yard drive following a Novo corner flashed inches wide.
Two minutes later at the other end Garry Brady was through on a Billy Mehmet flick only to shoot into the side-net.
The home side were right back in it - Andy Dorman testing Allan McGregor in 52 minutes with an angled log that the goalkeeper touched over.
Sixty seconds later in a lightning break from the halfway line Novo released Lafferty only for the striker to blast the ball straight at Gallagher.
Thomson replaced Lafferty on the hour - and within sixty seconds Mehmet headed wide from a Brady cross with the goal at his mercy.
If that was a bad miss worse was the one by Novo in 65 minutes when he somehow headed over from a Thomson cross.
Seven minutes later Novo again had an effort blocked from a Miller cutback.
There was a welcome return for Steven Naismith - an injury absentee for three months - when he replaced Miller in 77 minutes.
The little Spaniard finally made the game safe in 86 minutes when he raced away on a long ball from Davis before netting from a tight angle via an upright.
In the dying minutes the Light Blue legions erupted as new of Hibernian's last-minute winner at Celtic Park filtered through.
Afterwards Walter Smith summed up:
"We started very well, scored, then had a couple of other opportunities. Credit to St. Mirren however who pressured us, although Allan McGregor didn't have much to do. The players have a good attitude and a winning mentality, although the squad has been stretched since the turn of the year."
ST. MIRREN Gallagher; Ross, Potter, Innes, Barron; Thomson (O'Donnell 68), Murray, Dorman, Brady (Dargo 75); Mehmet, Higdon
UNUSED SUBS Howard, Mair, Burns, Devlin, Ramsay
RANGERS McGregor; Broadfoot, Weir, Wilson, Papac; Novo, Davis, McCulloch, Whittaker; Miller (Naismith 77), Lafferty (Thomson 60)
UNUSED SUBS Alexander, Mendes, Smith, Fleck, Little
REFEREE Craig Thomson