Motherwell will face Stranraer or Hibs after beating Morton on penalties
Dundee United will play Aberdeen or Livingston after edging past Forfar
St Mirren to visit Kilmarnock or Montrose in last eight after beating Inverness CT
Motherwell 0-0 Morton
Motherwell just can't get going here. They haven't posed any kind of threat to the Morton backline and the Championship visitors look settled.
Still no shots on goal but Gus MacPherson will be happy with what he's seeing.
St Mirren 1-1 Inverness CT
This is an absolutely cracking cup tie.
St Mirren hit the woodwork not once but twice in quick succession.
Ilkay Durmus is thwarted by the bar with a lovely chipped strike from the edge of the area.
The rebound falls to Kristian Dennis, who hammers the ball off the base off the post and behind.
Motherwell 0-0 Morton
A great ball from Aidan Nesbitt, who has started brightly for the away side, finds Craig McGuffie at the front post, but the Morton man miscues his first-time finish under pressure.
Decent chance that for the visitors.
St Mirren 1-1 Inverness CT
Jon Obika leathers a 25-yard strike goalwards but Caley keeper Mark Ridgers keeps his eye on it and saves well.
Ilkay Durmus is subsequently flagged offside, denying the hosts a corner.
St Mirren 1-1 Inverness CT
Referee John Beaton calls a temporary halt with Cammy MacPherson taking a head knock in an aerial challenge.
Thankfully the St Mirren substitute is fine to play on after a couple of minutes' treatment.
Motherwell 0-0 Morton
No chances yet at Fir Park but the Championship side have started well.
Gus MacPherson's men look comfortable on the ball and are enjoying large spells of possession in the Lanarkshire sun.
Kristian Dennis
Image source, BBC SportAn instant reply from the Buddies as Kristian Dennis slams the ball home from 18 yards out.
It was great work from Jamie McGrath to pluck the ball out of the sky, beat his man and then slide it across for Dennis.
Game on in Paisley.
Nikolay Todorov
Image source, BBC SportThere's a shock on the cards as the Championship side take the lead!
After Jak Alnwick palms away a Daniel MacKay strike, St Mirren invite more trouble as they concede a needless corner.
And when the ball is swung in by Scott Allan, Todorov pounces with a back-post volley to break the deadlock.
St Mirren 0-0 Inverness CT
The hosts have made a change at the interval, with Cammy MacPherson on and Kyle McAllister's shift over after 45 minutes.
St Mirren 0-0 Inverness CT
Back under way in Paisley. Bring on the goals, please.
Motherwell v Morton (19:00)
Derek Ferguson
Former Rangers and Hamilton midfielder on Sportsound
Quote MessageYou can't discount Morton, I don't think there's too much between the teams tonight, especially with Morton having an experienced and wily coach in Gus MacPherson.
Motherwell 0-0 Morton
We're up and running at Fir Park...
HT: St Mirren 0-0 Inverness CT
St Mirren boss Jim Goodwin, serving the first game of his three-match touchline ban, has plenty to ponder after his side's first-half performance.
Image source, SNSMotherwell v Morton (19:00)
Albeit a round later, Motherwell's last Scottish Cup success way back 1991 came after they eliminated a second-tier Morton side on the way to Hampden.
Both sides played out a goalless draw at Fir Park, before a 1-1 draw at Cappielow in the replay resulted in a dramatic penalty shootout win for the Lanarkshire side.
A semi-final triumph against Celtic was followed by an epic final, as Motherwell came out on top in a memorable 4-3 win against Dundee United.
Not to get any Well fans' hopes up but, 30 years on, is that a sign?
Image source, SNSMotherwell are approaching the 30-year anniversary of their last Scottish Cup win
Motherwell v Morton (19:00)
Motherwell manager Graham Alexander tells BBC Sportsound: "We've prepared in the same way we would for any league game.
"There were no second thoughts about making any serious changes. All the Morton players will be motivated to turn over a Premiership team.
"We've got to make sure we do our job right. We've got the quality but it means nothing without the right approach."
HT: St Mirren 0-0 Inverness CT
Steven Thompson
Former Scotland striker on BBC Sportsound
Quote MessageIt's been very open but in terms of the better opportunities created, Inverness will feel they should be at least 1-0 up. If it wasn't for Jak Alnwick they certainly would be ahead
Motherwell v Morton (19:00)
Motherwell manager Graham Alexander makes just one change to the side that beat St Mirren last Saturday.
On-loan Hearts winger Jordan Roberts, who suffered an injury in the 1-0 win, is replaced with Barry Maguire.
Morton boss Gus MacPherson makes two alterations to the team that drew 1-1 away to Dundee.
Craig McGuffie and Reece Lyon come into the starting line-up in place of Luca Colville and Lewis Strapp.
It's been an entertaining opening half in Paisley. Both sides are having a go and have hit the woodwork, but are yet to find a breakthrough.
Inverness have shaded it, with Jak Alnwick saving well from Daniel MacKay, Nikolay Todorov and Scott Allan.
St Mirren have threatened too, with Kristian Dennis denied by the bar on the stroke of half-time and having an earlier shot saved.
Image source, SNSSt Mirren 0-0 Inverness CT
It's St Mirren's turn to be denied by the goal-frame as Kristian Dennis' close-range shot takes a big deflection and loops on to the bar.
The rebound is kind to Inverness as the ball drops into the arms of grateful goalie Mark Ridgers.
St Mirren 0-0 Inverness CT
Blow for St Mirren as midfielder Jake Doyle-Hayes can't continue from an earlier knock.
Defender Richard Tait is on in his place, with a reshuffle required from boss Jim Goodwin.