Rangers secured their place in the Petrofac Training Cup final after brushing aside St Mirren in a one sided match at Ibrox.
Jason Holt put the home side ahead in the first half with a well-worked effort.
Kenny Miller, Martyn Waghorn and Dean Shiels added to that in the second half to put the tie beyond any doubt.
It is a result that takes Mark Warburton to his first cup final as Rangers manager, against Peterhead.
A meeting with the League One side at Hampden Park was the prize for sides who faced each other in a miserable day on the south side of Glasgow.
Ian Murray's men went into this one in pretty poor form and well aware that they had beaten the Ibrox side only once in their last 17 encounters.
It was easy to see why because most the game had the feel of a mismatched training exercise.
Rangers brought Miller back into the side in place of Nathan Oduwa and the veteran striker looked lively and dangerous from the start.
His fellow front men - Martin Waghorn and Barrie McKay - helped him terrorise the Buddies' back four and only a couple of stunning saves from Jamie Langfield early on kept the score level.
The visitors were struggling to contain the Rangers onslaught, but when they did break free, the best they could muster was a fairly tame Stephen Mallan free-kick from around 30 yards out.
It was Holt, bursting through from the midfield, who finally breached a battered and bruised defensive line just after the half hour to put the home side ahead.
He expertly controlled an Andy Halliday through ball at the back post and he drilled low past Langfield at the goalkeeper's near post.
St Mirren injected some much-needed fight and bite into their play after the break and the home fans started to show signs of getting nervous.
Only the crossbar saved Rangers from a ferocious Stuart Carswell shot on 67 minutes, when the former Motherwell midfielder had goalkeeper Wes Foderingham well beaten from the edge of the box.
It was a reminder to those playing in blue that they should have had this game dead and buried instead of rocking against the ropes.
It jolted the home side back into life and substitute Shiels played a neat ball through to Waghorn on the left hand side and the Englishman picked out Miller on the six-yard line for a simple tap in.
Knowing it was all or nothing, Murray threw his men forward in search of the seemingly impossible, but they were punished by Waghorn and a Rangers third.
He picked up the ball 40 yards from goal, skipped past two defenders and lashed the ball low past Langfield to claim his 18th goal of the season.
Shiels compounded the Saints' misery with a deflected fourth in injury time.
- 23HoltSubstituted forShielsat 63'minutes
- 9MillerSubstituted forHardieat 78'minutes
- 19McKaySubstituted forClarkat 63'minutes
- 7McMullanSubstituted forMorganat 45'minutes
- 14MallanBooked at 73minsSubstituted forStewartat 85'minutes
- 18MclearSubstituted forThompsonat 72'minutes
- Bobby Madden
- Shots on Target