The hosts are saved by a lick of paint - and more Jak Alnwick heroics.

David Carson's rampaging run down the right-hand channel is halted 20 yards out but Inverness team-mate Scott Allan pounces on the loose ball to curl a strike towards the bottom corner.

It looks a goal, only for Alnwick to get the slightest of touches to send the ball on to the post.

Nikolay Todorov has Jak Alnwick sprawling at full stretch to thwart the Inverness striker's lovely turn and shot.

The ball took a knick off Conor McCarthy on its way, making Alnwick's save all the better.

St Mirren are inches away from the opener.

A superb pass out of defence from Kyle McAllister is taken down by Kristian Dennis, whose 10-yard strike deflects off Brad McKay and spins just past the post.

Ilkay Durmus has his dancing shoes on.

The St Mirren winger shows lovely footwork to outfox two opponents and set up a shooting chance on the edge of the box, only to send his curling strike too high.

This Inverness away kit really is quite striking.

No chance of a colour clash here.

And Neil McCann's underdogs have been pretty impressive in pink so far.

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No goals but plenty of entertainment in the end-to-end opening skirmishes.

St Mirren striker Kristian Dennis is next to have a go, firing straight at Mark Ridgers after the ball fell nicely to him 12 yards out.

Motherwell: Kelly, O'Donnell, Gallagher, Lamie, McGinley, Maguire, Crawford, Campbell, Lawless, Cole, Long.

Substitutes: Chapman, Dunne, Carroll, Mugabi, Magloire, O'Hara, Foley, Cornelius, Hastie.

Morton: McAdams, Ledger, Fjortoft, McLean, McGinty, McGuffie, Lyon, Jacobs, McGinn, Nesbitt, Muirhead.

Substitutes: Wylie, Oliver, Orsi, Strapp, Blues, Colville, Easdale, Hynes, McGrattan.

The visitors hit back strongly and Daniel McKay's near-post drive has to be shovelled wide by Jak Alnwick.

Moments later the St Mirren keeper punches clear from MacKay as Inverness keep up the pressure.

A careless pass out of defence from Scott Allardice puts Inverness in trouble.

The ball is intercepted by Jamie McGrath on the edge of the box, but the St Mirren talisman shanks his sidefooted effort wide.

St Mirren's first effort on goal is spectacular but wayward.

The hosts work the ball well to Kristian Dennis wide left and he digs out a cross met by Ilkay Durmus with an acrobatic overhead kick that flies over the bar.

A positive opening from the Championship visitors as they start on the front foot.

Sean Welsh plays in Daniel MacKay for a pop at goal on the left edge of the box, but the youngster gets his timing all wrong and takes a fresh-air swipe.

It's a glorious night for football, with the Paisley pitch bathed in sunshine.

After a minute's silence in memory of Prince Philip, the Scottish Cup fourth round is under way.

The quarter-final draw has already taken place, so all six sides in action tonight know their potential opponents.

Either St Mirren or Inverness CT face a trip to Kilmarnock or Montrose.

The winners of Motherwell v Morton will be away to Stranraer or Hibernian.

And if Dundee United dispose of Forfar, they will visit Aberdeen or Livingston in an all-Premiership tie.

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These sides last met 34 years ago in a Scottish Cup quarter-final that went to a replay, with the tie sandwiching United’s 2-1 away win over Barcelona.

Four days after a 2-2 draw at Tannadice - with a 90th-minute penalty leveller - United went to the Nou Camp in the Uefa Cup last eight and won 2-1.

They then lost 1-0 at Rangers to Tannadice before winning the replay 2-0 at Station Park. But only after second-tier Forfar missed two penalties in a minute.

Motherwell are free to focus fully on the Scottish Cup after all but securing Premiership survival last weekend.

Graham Alexander's men began their trophy quest by easing past Formartine United 5-0 and have collected four wins from five to approach this tie in fine fettle.

Morton's visit to Fir Park provides respite from their Championship survival fight, with Gus MacPherson's men in the relegation play-off spot on goal difference.

They have faced Motherwell three times in the past six years, all in the League Cup, and claimed a 3-2 home win before twice losing 4-0 in Lanarkshire.

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Dundee United manager Micky Mellon has been linked with the Doncaster Rovers job in recent days, but his stock will plummet should his side fail to make it past League 1 bottom club Forfar.

Since last winning the Scottish Cup in 2010, United have reached one final and a couple of semi-finals.

With survival guaranteed in their first season back in the top flight, a good cup run would make it a more than decent campaign for Mellon's men.

Managerless Forfar have it all to do. But they'll have top-flight experience in the dugout with former Aberdeen assistant Tony Docherty lending a hand to interim boss Gary Irvine.

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In-form Inverness have already claimed a Premiership scalp on their travels as they attempt to repeat their unlikely Scottish Cup success of 2015.

The Championship side turfed out derby rivals Ross County 3-1 in a third-round 'El Kessocko' a fortnight ago and are flying for the trip to Paisley.

After a five-game winless start to Neil McCann's caretaker tenure, Inverness won six on the spin before a draw at Queen of the South last weekend.

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Kick every ball and watch all the action live from Forfar v Dundee United by clicking the link at the top of this page at 19:45 BST.

Before that, Radio Scotland MW has you covered with commentary of St Mirren v Inverness CT from 18:00.

There's also live online-only commentary on the BBC Sport Scotland website of Morton's trip to face Motherwell (19:00).

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St Mirren are eyeing a second trip to Hampden this season after their League Cup glory bid was ended in the semi-finals by Livingston.

That defeat stung, but Jim Goodwin's side proved they are a match for anyone, knocking out Rangers in the last eight in what remains the Ibrox men's only domestic defeat this season.

The Paisley men have tasted Scottish Cup success three times, most recently back in 1987 with a team containing current chief executive Tony Fitzpatrick.

Matching that triumph would make legends of Goodwin's current crop.

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St Mirren manager Jim Goodwin opts to make three changes from his side's 1-0 defeat to Motherwell at the weekend.

Out go Ethan Erhahon, Ryan Flynn and Lee Erwin, in come Kristian Dennis, Kyle McAllister and Jonathan Obika in an attacking looking line-up.

Inverness Caley hand a start to Sean Welsh, with Roddy MacGregor dropping out from the 1-1 draw with Queen of the South.