The 22-year-old hadn’t featured in almost nine months after suffering a cruciate ligament injury when these two sides met at the semi final stage of the same competition back in April.
Naismith completed 70 minutes of a match that lacked a great deal of goal mouth action but remained a nervous one for Rangers while the difference between the teams remained at a single goal.
The relief was evident when Naismith’s replacement Nacho Novo added to Stuart McCaffrey’s own goal when he slotted home Steven Davis’ square pass.
While Rangers finished the stronger, it was the home side who enjoyed a lively start.
Gavin Swankie tested Allan McGregor with a free kick in the second minute and Chris Millar picked up a yellow card a minute later for a foul on Pedro Mendes.
St Johnstone continued to threaten in the first quarter with Liam Craig twice having a go from distance when he forced McGregor in to action again, with the Gers keeper tipping over the bar.
McGregor was then grateful in the 22nd minute when he watched a Craig volley fly narrowly wide of his upright.
The visiting side had cause again to thank their shot stopper ten minutes later when he got down well to block from Andy Jackson, after Derek Holmes had nodded in to his path.
The value of those stops was evident with just three minutes of the half remaining as Gers broke the deadlock.
Naismith’s cross from the left was far too high for its target, Kris Boyd. But with the front man hunting the ball wide on the right Alan Main left his goal to try to clear.
The keeper’s attempt was poor and allowed Davis to knock the ball back to Boyd to deliver a cross.
His target was strike partner Kenny Miller, and while the Scotland man’s extravagant flick didn’t come off it did enough to bamboozle McCaffrey who turned the ball in to his own net.
It was just what Walter Smith’s side needed and they returned for the second half with renewed purpose.
Naismith almost settled the tie in the first minute of the second period when he broke on the left and switched to Davis, but the Northern Ireland international sliced his shot wide of Main’s post.
While Saints didn’t produce much of a threat to McGregor’s goal in the second 45 minutes, there remained an air of nervousness until Novo’s 78th minute contribution.
With the game all but over, Smith took the opportunity to introduce Lee McCulloch and John Fleck late on as replacements for first choice front pair Boyd and Miller.
It was Fleck’s first run out in the top team since the final of this competition last May, but he had little chance to make an impact as his side played out time and set up a 5th round meeting with Forfar.