St Mirren's "siege mentality" helped them bounce back from their League Cup exit by thumping Dundee United in the Scottish Premiership, manager Jim Goodwin says.

Joe Shaughnessy headed in the opener before Jamie McGrath dispatched two controversial penalties.

Ian Harkes' 30-yard stunner provided United hope early in the second half, but they never threatened a comeback.

Substitutes Dylan Connolly and Kristian Dennis rounded off a deserved win.

"We've had to go through a lot of ups and downs this season, with lots of different things and off-field issues and bad press about the club," Goodwin told BBC Scotland.

"I have to give great credit to the players, staff and people up the stairs to affect us. We've gained a siege mentality if you like and I'm just really pleased for the boys."

St Mirren have 11 games before the Premiership splits into two for the last round of games and Goodwin wants his players "to go into every single one of them with the mindset of trying to win". "Draws are no use anymore and that was our attitude tonight," he said.

The win puts St Mirren two points behind United with three games in hand as they maintain their charge for a top-half finish, the perfect antidote to Sunday's agonising semi-final loss to Livingston.

Micky Mellon's United, meanwhile, are now without a win in six league games, albeit this is just their second defeat in that run.

They started slowly but ought to have gone ahead through Dillon Powers as the American forced Jak Alnwick into a brilliant reaction save before turning the rebound over the bar from just seven yards.

However, that was the extent of United's threat in the opening 45 minutes as St Mirren caused problems with their deliveries into the box.

McGrath's deep free-kick was flicked on by Conor McCarthy and Shaughnessy was lurking at the back post to head home.

It was probably a deserved lead for St Mirren, who had not won at Tannadice since 2012, but the whole complexion of the game turned on the two penalty calls by referee John Beaton.

Centre-half Mark Reynolds was left stunned at the sound of the whistle after Shaughnessy fell to the ground following a slight nudge - and penalty specialist McGrath stepped up to roll the spot kick into goalkeeper Deniz Mehmet's left-hand corner.

Then, three minutes later, another delivery into the box was headed to the feet of Ryan Flynn, whose thumping shot struck the raised - but tucked in - arms of Lawrence Shankland for another spot-kick. McGrath found the other corner with another precise finish.

One can only imagine the scenes in the home dressing-room at the break and Mellon replaced Powers for academy graduate Kai Fotheringham. The United manager would have at least enjoyed watching Harkes' glorious effort.

The American midfielder swept Luke Bolton's pass right into the top corner to leave the impressive Alnwick rooted to the spot. It jolted United to life, but only for a brief spell before St Mirren regained complete control.

Dennis and Connolly both went close before eventually finding the net to add gloss to the scoreline.

Connolly outstripped Liam Smith to latch on to a through ball and loft a delicate finish over Deniz before Dennis tapped home from point-blank range after a surging run by Flynn, who was playing his first match for 11 months following a cruciate injury.

The victory ended a run of 10 losses and one draw at Tannadice for St Mirren, who are now breathing down United's neck in the race for the top six.

Man of the match - Jamie McGrath

What did we learn?

St Mirren were the lowest scorers in the Premiership coming into this match, with just 16 goals in 21 matches, but the general sense is that they are capable of a top-six finish. McGrath has been a transformational signing with his quality in midfield - and the return of Flynn is a boost.

They look like a side who are building on solid foundations laid earlier in the season, while the opposite could be said of United. St Mirren were the only side with a lower goal tally than Mellon's men, who are yet to figure out how to get the best out of Shankland and Nicky Clark up top.

Of the 19-strong matchday squad, 17 were with the club in the Championship last season - and it showed. If they start conceding goals at this rate, they will be in danger of a relegation scrap.

What they said

Dundee United manager Micky Mellon: "A lot of things went against us. Soft penalties which are going to change the course of the game, and chances missed at vital times."

St Mirren manager Jim Goodwin: "It takes a bit of courage to give two [penalties] in one game, but I felt they were obvious. We could've done with John [Beaton] on Sunday in the semi-final.

"It was a really great performance all round, in terms of the reaction from the players."

What's next?

United host Hibernian at Tannadice on Saturday (15:00 GMT), while St Mirren are away to Celtic at the same time.