His men weren’t always at their best against Nine in a Row legend Stuart McCall’s side at Hampden despite leading twice.
Even so, enough was done to put Smith into his 16th final and he’ll have to go through yet another Old Firm derby if he is to taste success in the event for the 12th time.
That match will come on March 20, meaning the SPL trip to Aberdeen the day before will now be rescheduled.
The manager made three changes to the team which won 2-0 at Hibernian in the SPL courtesy of goals from Madjid Bougherra and Nikica Jelavic.
As expected, Neil Alexander came in for Allan McGregor in goals while Jamie Ness and Vladimir Weiss also made way for Edu and Kyle Lafferty.
That meant Naismith dropped into a left midfield role, with Lafferty partnering Jelavic in a two-man attack.
It was the Steelmen who had the first opportunity when Jamie Murphy found space down the left and warmed Alexander’s palms with a well-hit but poorly-directed drive.
Lee McCulloch responded at the other end after some good build-up play by Gers but his final effort flew high and wide of the target.
Otherwise, it was a fairly low-key opening passage of play but it was the Light Blues who enjoyed most possession.
And they almost broke the deadlock through McCulloch when he shot wide after a neat move involving Edu and Jelavic.
Back came Well, with John Sutton undoubtedly feeling he could have done better than direct a tame header from Chris Humphrey’s cross straight into Alexander’s grasp.
Steven Whittaker had the best chance so far when his rasping free kick was deflected only just over by the wall following a foul on Jelavic.
And moments later, with 19 minutes gone, the SPL champions took a lead they deserved on the balance of play.
Edu was the scorer, turning the ball on to his left foot and rifling home from the edge of the box across Darren Randolph.
It was a fine finish and one the American enjoyed as he ran to celebrate with fans sitting in the North Stand.
Motherwell’s response was anything but immediate and Rangers continued to dictate play as the game trundled along at a somewhat pedestrian pace.
When the Lanarkshire outfit did catch sight of goal, Tom Hateley was off range as his ferocious shot from 20 yards kept on rising well after it cleared the crossbar.
Steven Davis might have added to Gers’ lead when he took advantage of Shaun Hutchinson’s poor clearance but Randolph smothered at his near post.
Steven Hammell was just as unlucky for the Fir Park team with a free kick from distance as Alexander got down well to keep it out.
With half-time approaching, Well settled down and began to find their rhythm a little more and Murphy had a go once more but couldn’t test Alexander.
Edu then tried to double his and his team’s tally when the ball broke to him after Jelavic failed to control although Randolph was equal to it.
Play was swinging from end to end and the small band of fans who had come from Motherwell began to sense their team was in contention.
But it was still 1-0 at the break and it took the best part of quarter of an hour for anything of great note to happen after the restart.
When it did, however, it took good reactions from Alexander to deny Steve Jennings from 25 yards as his rising strike arrowed towards the top corner.
Well were getting closer and midway through the second half they got their reward after continually chipping away.
Keith Lasley was the man who got them back in the game, sending a crisp daisy-cutter beyond Alexander to make it 1-1.
Suddenly Gers were on the ropes having been in control for much of the afternoon but they lacked imagination as they went about trying to regain the lead.
Bougherra charged forward in a bid to spark Smith’s side into life and he won a corner, from which McCulloch headed a yard over.
Substitute John Fleck – on for the quiet Lafferty – then played a neat one-two with Davis which culminated in the Northern Ireland midfielder shooting past the post.
Now Rangers were in the ascendancy and Jelavic, whose workrate was keeping the Well defence on its toes, pulled a shot well wide.
While he unsuccessful there though, the Croatian was instrumental in getting the trophy holders back on top 15 minutes from full time.
Jelavic took possession on the left flank and with a stepover one way and a dip of the shoulder the other, he muscled past his marker and crossed into the box.
Waiting there gratefully was Naismith, who headed his ninth club goal of the season into the net to score for the first time in almost three months.
With that, the ball was back in Motherwell’s court and they gave it their best shot at equalizing for a second time as they piled on pressure in the closing stages.
Sutton forced a good point blank save from Alexander moments from the end after a series of corners.
And then, after the Rangers defence couldn’t clear, the former St Mirren forward hit the target again but couldn’t find a way past the keeper.
Naismith had a late chance to put gloss on the win after being set up by Weiss, on as a late replacement for Jelavic.
But although his final effort was weak, it didn’t matter in the end and the Ibrox team now have another derby to look forward to.