
St Mirren scored three past Motherwell for the second time in a week as they progressed to the Co-operative Insurance Cup semi-finals.
Michael Higdon rose to powerfully head Andy Dorman's cross past Steelmen goalkeeper John Ruddy on 23 minutes.
Jack Ross doubled the home side's advantage with a venomous shot which took a deflection on 61 minutes.
With nine minutes remaining Dorman ran from his own half before his cross went in off Motherwell's Stephen Craigan.
Motherwell started in a more positive manner than they had done on Saturday, when they needed a late Lukas Jutkiewicz double to rescue a point in a thrilling 3-3 league draw.
Winger Jim O'Brien was quickly to the fore and his 25-yard strike was parried wide by Paul Gallacher in the eighth minute.
However, the visitors soon repeated their worst trait of Saturday by conceding possession inside their own half.
Dorman could not get enough power in his 20-yard strike after Hutchinson's throw had put Tom Hateley in trouble and John Ruddy's deflected clearance fell kindly for the visitors after Billy Mehmet had closed the goalkeeper down.
Saints kept up the pressure and Higdon gave them a 23rd-minute lead.
The striker's header spun over the line off the hand of a diving Ruddy after an in-swinging free-kick from Dorman, who had been brought down by Yassin Moutaouakil.
Gallacher dived to hold Jamie Murphy's low strike from 20 yards as Motherwell tried to hit back immediately.
But they struggled to break through an organised St Mirren side and the hosts looked dangerous when Dorman broke from midfield.
Shortly after the hour mark the hosts doubled their advantage when full-back Ross advanced to take a shot which took a deflection on its way past Ruddy.
And in the closing stages Dorman capped a good night for him and his team, finishing off a run from his own half with a deflected goal off Steelmen captain Craigan.
St Mirren manager Gus MacPherson:
"In the last few games we have taken our chances and we got the goal at a good time tonight.
"That settled us down, but then Motherwell came at us and we've Paul Gallacher to thank for making a crucial save for us. We went from strength to strength after that.
"The players and the fans now have a semi-final to look forward to, but the message we've given to the team after the game is that the preparation starts now for the next league game."
Motherwell manager Jim Gannon:
"We had chances and maybe if we'd got a goal we would have given them a better game.
"Overall they showed much more solid technique, better passing, better deliveries into the box and they got their goals.
"It was a good performance from them and they deserve to be in the hat for the next round, so good luck to them.
"We changed the shape a bit after Saturday, but you felt at the start that there wasn't enough energy and quality about our game to deserve anything on the night."