THEY say that one man's misfortune is often another man's gain and so it proved in Paisley as St Mirren booked their place in the fifth round of the William Hill Scottish Cup.

Paul McGowan will find out today the seriousness of a foot injury sustained in Saturday's goalless draw with Inverness Caledonian Thistle, with early fears he could be out for as long as 10 weeks. In from the cold to replace him came Gary Harkins for his first start since September 21, the forward scoring the opening goal as Danny Lennon's side finally saw off the threat of Queen of the South at the second attempt to book an away tie against Dundee United.

Harkins had struggled to make the impact initially expected of him after his summer arrival from Dundee, his relegation to the bench coinciding with St Mirren belatedly emerging from their early-season slump. He seemed of a mood to make the most of a rare opportunity last night, in the first half especially, unleashing an audacious shot from 40 yards that drifted wide before a run into the box concluded with a sidefooted an effort that drifted well off target. Should McGowan be sidelined for any period of time then Lennon will surely be happy to have a confident and in-form Harkins as his replacement.

The Paisley side ran out fairly comfortable winners in the end but only after allowing Queen of the South back into things early in the second half with the score still 1-0. Having failed to beat their opponents from the SPFL Championship on any on the three occasions they had faced them on their artificial surface earlier in the campaign, Lennon and his players had confidently predicted it would be a different story on grass and in front of their own fans. Instead St Mirren made heavy weather of it for a spell after failing to make their first-half dominance count.

They had to survive some sustained Queen of the South pressure before a second goal after 73 minutes made sure of the win. A third, a stunning strike from substitute Sean Kelly that ripped into the top corner, was almost harsh on Queens given all they had contributed to both matches of the tie. "In the second half we started really well and took the game to St Mirren and I thought they scored against the run of play," said Jim McIntyre, the Queen of the South manager. "When you're having a period [of supremacy] you have to put the ball in the net and it would have been interesting to have seen the reaction then. Three-nil flatters them in my mind but they got the job done and we never."

Harkins made a positive contribution on his return to the side although there was a touch of good fortune about his goal after 18 minutes. He made a complete hash of his first effort after fastening on to Steven Thompson's knockdown only for the ball to sit up nicely as if to say, 'have another bash'. This time he made no mistake. Harkins passed up two further chances - one that he ought to have scored - but he was not alone in that regard as St Mirren endured a wasteful first half. Kenny McLean had a shot saved, John McGinn's deflected cross ran across the six-yard box with no one there to stick it in, before the same player had a header tipped around his post by Zander Clark in the visitors goal.

Little had been seen by Queens in a positive sense by that point although one attack late in the first half almost paid dividends, Derek Lyle's hitch-kick volley clunking against the top of the crossbar and dropping over the top. They threatened again within 30 seconds of the second half, Danny Carmichael crossing for Iain Russell who scooped his shot over.

That led to an extended period of Queens pressure for the first time in the match as they forced a number of corners in the hope of bringing about an equaliser. Russell, who had scored in the original tie, again came close, his shot clipping off Marc McAusland and spiralling just over, before Lyle connected with Ian McShane's deep free kick at the back post but could not get his effort on target.

St Mirren survived the onslaught then came again, finding two goals to secure their passage. McAusland seemed to slip as he went to shoot but the ball ricocheted against Kevin Holt and fell kindly for Thompson who lashed it past the unfortunate Clark. Kelly's goal, his first for the club, sealed the win four minutes from time, the full-back collecting a pass from Conor Newton and hitting it first-time beyond the goalkeeper.

"It was another stern test for us tonight against a very good Queen of the South side," said Lennon. "I'm delighted to come through it. That's our fifth clean sheet in nine games so that shows how well we're defending."