Sasa Papac relieved the nerves for the home side just after the half hour mark but after Darren McGregor’s quick response it took a Steven Whittaker penalty in the second period to get the Light Blues back in front.
Shorn of Steven Naismith through suspension Smith introduced El Hadji Diouf to replace the Scotland international.
Richard Foster also returned after being ineligible at Pittodrie on the previous Wednesday with Gregg Wylde dropping to the bench.
Joining the youngster in the dugout was the returning Madjid Bougherra, not deemed ready for a start after a lengthy lay off with a hamstring injury.
It seemed Bougherra would not be missed in the early stages as central defensive pairing Davie Weir and Steven Whittaker were rarely troubled by St Mirren.
The majority of the opening 15 minutes were spent in the Saints’ half with El Hadji Diouf and Nikica Lafferty stretching the visitors’ backline.
They were being well supported by Kyle Lafferty who had moved out to the left flank to fill the gap left by Wylde.
And the Ulsterman had the ball in the net midway through the half, but despite the neat build up from Steven Davis and Diouf the goal was disallowed for offside.
It was a tight call, but one that the officials got correct. Lafferty was denied again just after the half hour, but his deflected effort did lead to the Light Blues’ opener.
It was the unlikeliest of sources that got Rangers in front but much of the credit for the goal goes to Davis.
The Northern Ireland man did superbly to win back possession on the right flank when St Mirren looked likely to clear.
He exchanged passes with Diouf on the flank and when he found the space he picked out fellow Ulsterman Lafferty.
Lafferty had a decent effort well blocked and Papac was on hand to knock the ball in to an empty net for a third of the season.
That seemed to settle the nerves in the Ibrox stands, but the comfort didn’t last long with Darren McGregor bursting forward to good effect for the visitors.
He left a couple of Rangers players trailing to make his way in to the box and meet Aaron Mooy’s cross from the right.
It was a fine finish for a central defender but one that could have been avoided from the home side’s point of view.
McGregor was allowed to travel far too far without being tracked and Walter Smith will no doubt have made that point in his half time team talk.
And it seemed to spark the right reaction from his side which was far more purposeful in the early stages of the second period.
That purpose paid off when Nikica Jelavic earned his side a penalty just six minutes in to the half.
He turned brilliantly after picking up Lafferty’s flick on and suckered John Potter in to a foul for which the defender was cautioned.
Penalty duties again fell to Whittaker who produced the perfect balance of pace and placement to wrong foot Paul Gallacher in the Saints goal and restore his side’s lead.
Jelavic was evidently in the mood, encouraging his side from the kick off following the second Gers goal and he was involved again five minutes later.
He showed great footwork on the edge of the area to feed Foster on the right, and the Croatian was in position to get on the end of the on-loan defender’s cross.
Unfortunately the £4million man was unable to get his header on target but he was becoming increasingly influential.
He was unfortunate to be denied another chance with a little over twenty minutes remaining when he combined really well with Diouf on the Rangers left.
The Senegalese forward played a superbly weighted pass through for his strike partner, but just as he looked like he would pull the trigger Potter did well to block.
Having popped up on the left, Jelavic was at it again on the opposite flank with Davis this time the creator-in-chief.
The pair exchanged brilliant first time passes to set the striker down the right and his cross was again well defended by the visitors, this time denying Diouf.
With none of those chances taken it made for a nervy closing period for the home side, with Jamie Ness feeling the effects of a hard shift in midfield.
He was replaced by Kyle Hutton with just four minutes remaining after what appeared to be a case of cramp in his calf.