The defeat ends the side’s bid to reach the last four of the competition and was made all the more frustrating given the Gers took the lead in the contest through a terrific strike from Kyle Glasgow.
However, the Paisley outfit continue to prove a thorn in Rangers’ side this season, levelling before the interval through Thomas Falconer before a Luke Douglas penalty and goals from Jude Freel, Joshua Farquhar and Innes Clark took the game away from the home side.
It was a harsh reflection of the contest given the quality of chances created by the home side who were punished for their lack of clinical edge.
Rangers will conclude their group stage fixtures with the visit of Hibernian next week before attention then returns to league action, with Rangers in the hunt for the title, with a home clash against Motherwell in nine days' time.
Malky Thomson made three changes to his side from Saturday’s victory over Kilmarnock in league action, with Jaden Millarvie replacing the absent Sam Reid between the posts alongside starts for the 2010-born duo of Ashton Scally and Luca Rankin.
Rangers began the brighter of the two sides but were forced into some diligent defending when the visitors broke forward and James Reid, making his second successive start, produced a vital block to deny a goalbound effort.
The hosts certainly looked more assured in possession and were moving the ball crisply through the thirds, particularly down the left-hand side and through the lively combination of Ashton Scally and Max Cameron.
Indeed, a driving run from the latter almost engineered an opening goal on 20 minutes when he hit the byline and clipped a wicked cross into the six-yard area which was inches away from being turned home inadvertently by a St. Mirren body.
The Gers’ early pressure soon told as they cracked open the contest with a perfectly designed move.
It began midway inside their own half when Scally swivelled smartly away from pressure, bursting into the vacated space before switching the point of attack to Glasgow on the opposite side. His first touch immediately sized up the defender, and with the underlapping run of Calum Young providing a decoy the winger shifted the ball inside and slammed a delightful finish into the bottom near corner.
An immediate response was almost offered by the visitors when Lewis Hodgkiss broke through the Rangers rearguard with a smart run from midfield, but with only Jaden Millarvie to beat the goalkeeper stuck out his leg at the perfect moment to prevent a leveller.
Down the opposite end, Aiden Crilly drove an effort straight down the throat of the St. Mirren goalkeeper before Zebedee Lawson dug out a shot which was blocked in a crowded penalty area when the ball broke kindly to him from a free-kick delivery.
However, the Paisley side broke forward and dug out an equaliser when Millarvie done well to save initially before the Gers failed to clear their lines and a delivery from the right fell to Falconer at the edge of the penalty area and caressed the ball into the bottom corner.
Rangers perhaps ought to have restored their advantage before the interval when Lawson skipped through a succession of challenges before dragging an effort wide. Opportunity then beckoned for Cameron Fernie when he collected inside the penalty area but shot off target on his unfavoured left side.
The woodwork was rattling just moments into the second period when Cameron collected a pinpoint pass out of defence by Conor Owen before driving the length of the St. Mirren half and clipping the outside of the post from an acute angle.
It was certainly a competitive contest until that point, as meetings between these two sides this term have tended to be, as Millarvie clawed a trickling effort from Struan Thompson off the goalline before Lawson was thwarted by the feet of the St. Mirren goalkeeper after duking out his marker inside box.
Pressure was mounting towards the visitors’ goal as just moments later Glasgow was denied from a set-piece Rangers worked the ball patiently around the St. Mirren penalty area before Calum Young dragged an effort inches wide.
And yet it was the Paisley outfit who got their noses in front moments later from the penalty spot when Rangers were penalised and Douglas, sliding his strike from 12 yards fortuitously under the diving Millarvie, converted.
The Gers were still licking their wounds from the concession of a second when St. Mirren stretched their advantage and left the hosts with a mountain to climb. A cut-back from the left caught Millarvie stranded, and when the ball ricocheted wickedly back off the post Freel pounced to tap home from point-blank range.
A fourth for the away side arrived with a quarter of an hour to play when a dangerous inswinging corner sailed onto the head of substitute Farquhar who nodded home from close-range, before the scoring was rounded off when Rangers dropped their guard once again from a set-piece and Clark was on hand to finish.
RANGERS: Millarvie, Young, Reid, Owen, Scally (Wark, 75), Crilly, Rankin, Fernie, Lawson (Fergusson, 75), Glasgow, Cameron
Subs not used: Mames, Hynd, Hutton, Hall
ST. MIRREN: Tamosevicius, Barr, Falconer, Clark, Hutchison, Hodgkiss, McMillan, Thompson, Douglas, Freel, McCormick
Subs: Innes, Stoddart, McEvoy, Farquhar, Hunter, Rory, Duff
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