IF bottling up your emotions is unhealthy, expressing yourself is perhaps the best way to alleviate pressure.

After failing to record a victory since December 1 – or a league win since November 17 – Dundee had their fair share of pent-up frustration, and every drop of it was vented at Morton yesterday as they overcame a troublesome first-half performance to triumph 5-1, thereby booking a place against Dundee United at home in the quarter-final of the William Hill Scottish Cup.

The main protagonists may have been the same for the long-suffering Tayside support, but the plot was far from familiar as the entire Dundee cast finally changed a script that was grating with their loyal audience.

Despite the difference in status between themselves and their Irn-Bru First Division visitors, the safe progression of the Clydesdale Bank Premier League side had been in the balance to say the least. At half-time, with the game poised at 1-1, the twist in the tale remained a possibility.

The finishing of Barry Smith's men in the opening 45 minutes was typical of the form that has left his team languishing at the foot of the SPL, making them favourites to exchange league places with Morton in the summer.

Jim McAlister's low drive to open the scoring on 29 minutes aside, Dundee's weak efforts either trundled into the arms of grateful Greenock goalkeeper Derek Gaston or harmlessly by the post. Colin Nish struggled to control the ball, let alone divert it towards goal.

However, the interval afforded the Dens Park manager the chance to compose his beleaguered bunch. "We had more control in the second half," explained Smith. "We asked them at half-time to do things a bit differently – to move the ball more quickly, and get it forward with more urgency."

What a difference it made. Twenty minutes of pressure followed as Dundee's midfield – led by the imperious Nicky Riley – raised their game and their defensive line as Morton were pegged further back.

This proved critical as the visitors eventually cracked under the strain of defending a raft of set pieces, with four goals coming in a frantic 17-minute spell.

"If you have someone to pick up at a set piece, then it's your job to make sure they're not on the end of the ball," said Allan Moore, the Morton manager. His hopes of a positive outcome were raised after Michael Tidser poked home 90 seconds after the opener to level. "We didn't win the first header, and we didn't pick up the loose ball. Four goals from dead balls is not good enough."

As much as Dundee's finishing was clinical – or slightly comical in the case of Nish – after the interval, Moore correctly highlighted the defensive incompetence of his rearguard throughout this fifth-round tie, as it was that which afforded their opponents their chances.

The opening goal came from Nish rising high in the heart of the box to head a long ball to McAlister, who drifted away from his man to rifle a half-volley low into the net.

The next score arrived on 65 minutes as on-loan Celtic centre-half Lewis Toshney glanced McAlister's corner high into the net, while the third was headed home by Nish, although the former Kilmarnock forward knew little about it as the ball skimmed off Scott Taggart and in via his face.

The fourth arrived from a floated Kevin McBride free-kick which was nodded down by Nish for John Baird to smash home, and the rout was rounded off by Declan Gallagher's header at the back post on 82 minutes.

All in all, the afternoon allowed those of a Dundee persuasion to enjoy a rather unusual feeling as they bounced merrily out of Dens Park with the tune of the Great Escape blaring in the background. Whether that theme is continued on Friday night following their league encounter with Ross County will be the next defining act in Dundee's story this season.