Rangers cruelly exposed Dundee United's defensive frailties to set up a CIS Insurance Cup final with Motherwell.
Nacho Novo burst clear of the United defence to open the scoring after seven minutes and Dado Prso doubled the lead with a looping header soon after.
Novo missed a penalty and Jason Scotland pulled one back for United before Thomas Buffel bundled in a goal.
Fernando Ricksen curled in a free-kick before Steven Thompson scored a quick double and Novo grabbed his second.
A lively start saw Novo fire an overhead kick wide after Buffel's header across the box had taken a deflection off a defender.
But the little Spaniard did not take long to open his account when he used his quicksilver pace to convert a fine flowing move.
Prso's pass enabled Buffel to play a first-time ball beyond the United defence that Novo latched on to and, once he had taken the ball around the on-rushing Nick Colgan, he had no difficulty finding the empty net.
United had a good chance when Barry Robson made ground down the left but his cross was headed over on the run by Stevie Crawford from eight yards out.
Prso extended the Ibrox side's advantage in the 17th minute when he met a Marvin Andrews long free-kick with a diagonal header from 15 yards which went in off the far post.
There was little pace on the ball and Colgan was slow getting down to try and save.
United were in disarray at the back and there was a let-off when Novo scuffed wide from a promising position.
Prso then squandered a great chance when he failed to loft the ball over the stranded Colgan.
There was a further reprieve for Ian McCall's team when Novo's weak penalty kick was easily saved by Colgan in the 38th minute.
The award had been given following a tangle between Paul Ritchie and Prso and looked very soft.
United, who had not troubled new Rangers keeper Ronald Waterreus in the first half, pulled a goal back five minutes after the interval.
An Andrews tackle on Jim McIntyre broke to Scotland and the substitute drilled the ball home from 12 yards.
The Tannadice side were unfortunate not to be level when McIntyre's powerful strike from 25 yards hit the post, cannoned along the goal-line and bounced out off the other post.
United were then denied what looked a certain penalty when Crawford's close range shot on the turn was blocked by the outstretched arm of Andrews.
Rangers were enduring a torrid time of it and Waterreus had to make a flying save to keep out a 20-yard shot from Mark Kerr.
However, Buffel was able to restore Rangers' two-goal cushion when he forced in a fierce low cross from Novo after 67 minutes.
A minute later, the Rangers support were on their feet welcoming former skipper Barry Ferguson into the fray.
They were celebrating again when Fernando Ricksen curled in a free kick from 20 yards and Thompson smartly converted a Maurice Ross cross on the half-volley.
Novo then fired past Colgan with the United defence posted missing and Thompson was on hand to fire in goal number seven after Colgan spilled a shot from Ferguson.
Rangers: Waterreus, Ross, Andrews, Kyrgiakos, Ball, Ricksen, Alex Rae (Ferguson 69), Vignal, Novo, Prso (Thompson 75), Buffel.
Subs Not Used: Malcolm, Graeme Smith, Namouchi.
Goals: Novo 7, Prso 18, Buffel 67, Ricksen 77, Thompson 80, Novo 85, Thompson 88.
Dundee Utd: Colgan, Mair (Dodds 75), McCracken, Ritchie, Archibald (Duff 45), Wilson, McInnes (Scotland 45), Kerr, Robson, Crawford, McIntyre.
Subs Not Used: Grady, Bullock.
Booked: Kerr, Archibald.
Goals: Scotland 50.
Ref: H Dallas (Scotland).