With St Mirren seven points adrift at the foot of the Championship and Dundee unbeaten at home since October proceedings at Dens Park had all the makings of a shock only because there was absolutely no reason for the vast majority of us to anticipate this outcome.

Not that Jack Ross, the St Mirren manager, seemed to doubt that his side was capable of a win earned by a first half goal from ex-Dundee striker John Sutton and a second early in the second half from central defender Jack Baird.

“I was pleased for them because that group has endured a difficult season,” he said.

“They’ve come in for criticism on a regular basis so to get the rewards for their performance, when they haven’t always had that over the past two or three months, they should enjoy this day, look back on it tomorrow, then come back and try to replicate it in league games.”

He noted that, apart from their poor performance against Queen of the South and a meeting with Morton soon after he was appointed in October, they have generally deserved better during his time in charge.

However their cause was helped significantly by the contribution of new signing Billy O’Brien, the on-loan Manchester City goal-keeper pulling off fine saves to deny Craig Wighton and Marcus Haber and keep his side in front at the break.

“We haven’t always gained as many points as I think we deserved, so today we got both things right, the result as well as the performance and the clean sheet makes a difference because we’ve not had very many of them this season and that makes it difficult to win games,” Ross observed.

By contrast while Paul Hartley, his Dundee counterpart, offered credit to the visitors, he had clearly seen this tie as the ideal platform for a moral boosting cup run so was dismayed by his team’s showing and unprepared to offer his players any sort of excuse in the shape of the Premiership winter break which has, in the past, been the precursor to surprises in this competition

“It was a performance that was totally unacceptable because it was one that we didn’t see coming,” he admitted.

“It was the same team that performed against St Johnstone before the break and to go out (of the cup) at the first hurdle is not an acceptable result for us.

“We’ve trained hard, we’ve trained well, it’s been excellent. The players looked good, they looked sharp, they just weren’t on it today.”

The opportunity for the opener was created by Stevie Mallan driving at the defence, as he and his well organised team-mates did with gusto did at every opportunity in the first half in particular, forcing Dundee captain Paul McGowan into a challenge. Admittedly they got a break at that point, the ball ricocheting towards the home team’s penalty area where Sutton ran onto it and calmly passed the ball round Scott Bain and just inside the goal-keeper’s left post in the manner to be expected of a finisher with his track record, given time and room.

Good fortune also contributed to their second as, when the ball broke to him following a St Mirren corner early in the second half, Craig Wighton should have had no trouble clearing it on the right edge of his penalty area. However he slipped as he made to gather it, gifting possession to Mallan who cut it back into the path of Baird and his sweetly clipped shot, high to Bain’s left, gave the visitors the reassurance they needed to ease their way to victory.

Dundee: Bain, Kerr, Etxabeguren, Gadzhalov, McGowan capt, Hateley (Duffy 57), El Bakhtaoui (Williams 57), O’Hara, Wighton

St Mirren: O’Brien, Fjelde, Baird, MacKenzie, Irvine capt, Storie, McAllister (MacPherson 90+2), Magennis (Whyte 74), Mallan, Morgan, Sutton (Clarkson 90+4)

Scorers: Sutton 24, Baird 48

Referee: B Madden

Attendance: 3622