Thistle are playing some excellent stuff going forward, with Tony Watt involved again to pick out Aidan Fitzpatrick.

He's through one-on-one and slides his shot wide. That was an excellent opportunity to effectively end the tie there.

Another Motherwell chance goes begging.

Tawanda Maswanhise shoots straight at Toby Steward in the St Johnstone goal.

Motherwell fans must be tearing their hair out.

Another chance goes begging after tidy build-up play.

Apostolos Stamatelopoulos is in on goal, but his first touch is heavy and forces him wide, allowing St Johnstone to get back and avert the danger.

Image source, SNS

Aberdeen make a couple of changes. Teenager Fletcher Boyd is on, as is Topi Keskinen. Shayden Morris and Nicolas Milanovic make way.

So a change on both flanks and they're both into the action straight away.

Boyd has his fierce shot is parried away by James Storer after Keskinen is also denied by the Morton goalkeeper. The Finn probably should have squared it there.

Brian McLauchlin
BBC Scotland at Smisa Stadium, Paisley

Hearts boss Derek McInnes might not wait too much longer to make further changes.

Meanwhile Stephen Robinson, looks very happy and content with how his team have started the second half.

Next goal crucial!

Image source, SNS

On-loan Ayr midfielder Kyle Ure lunges in late at the feet of Tsoanelo Lets'osa.

Plenty of red card shouts from players and punters alike, but he is shown only a yellow card for the rash challenge.

Tyrone Smith
BBC Scotland at McDiarmid Park

Motherwell were claiming for a penalty a few moments ago when Stephen O’Donnell went down in the box.

But instead of awarding a spot kick, referee David Dickinson booked the player for simulation.

Andy Burke
BBC Sport Scotland at Cappielow

Kusini Yengi has looked far from convincing in his early outings as an Aberdeen player, but there have been signs here this afternoon that he may just be finding his feet.

Admittedly the opposition is a step down from what he has faced already in Hearts and Celtic, but the big striker has showed some neat touches, good link-up play and a bit of physical presence.

He's also got his goal, and while it was the easiest of tap-ins, it might just be the confidence boost he needs.

Image source, SNS

Hearts goalkeeper Zander Clark denies Killian Phillips after a stinging half-volley by the St Mirren midfielder.

That one was swerving.

Great defending from Cheick Diabate, who turns a dangerous Motherwell cross behind for a corner.

Apostolos Stamatelopoulos was lurking behind the Saints defender.

Morton have started the second half brighter, getting some territory to launch some crosses into the Aberdeen box.

A goal for the Greenock side would change the mood in the Wee Dublin end, where the Aberdeen fans are housed, significantly.

Four changes at half-time, two of them unsurprising.

St Mirren left-back Declan John, who was booked in the first half, is replaced by Scott Tanser.

It's a similar story for Hearts midfielder Tomas Bent Magnusson.

Wingers Pierre Landry Kabore and Alexandros Kyziridis also make way, with Beni Baningime, Claudio Braga and Elton Kabangu introduced by the visitors.

Tyrone Smith
BBC Scotland at McDiarmid Park

St Johnstone boss Simo Valakari is set to ring the changes with Uche Ikpeazu and Reghan Tumility being readied to come on.

We are back under way at Cappielow, with the other ties not far behind.

Later today. It takes place following Rangers' match with Alloa, which kicks off at 17:45 BST.

The last-eight ties are due to be played on the weekend of 20/21 September.

Brian McLauchlin
BBC Scotland at Smisa Stadium, Paisley

A one-goal advantage is the least St Mirren deserve after a dominant performance against a sluggish Hearts.

The message from Stephen Robinson to his players at the break will be 'same again please', while Derek McInnes will no doubt have some strong words for his players who have been outfought throughout.

I would expect some changes at the break as they simply cannot allow the Buddies to get a second.

Image source, SNS

Andy Burke
BBC Sport Scotland at Cappielow

Who described this as a potential banana skin? Can't recall, but it's been anything but so far.

Aberdeen have controlled the game, dominated the ball and are worthy of their two-goal lead at the break.

Morton defended well for the first half hour, but with what little ball they've had they've been pretty wasteful.

Dougie Imrie will be urging his players to at least give Aberdeen something to think about in the second half.

Hearts defender Craig Halkett picked up a nasty head gash in the first half and will be bandaged up for the remainder of the game.

Image source, SNS

A very forgettable first half comes to a close.

Motherwell have played some good stuff at points but offered little in the final third, while the home side have offered a threat on the break.

Neither goalkeeper has had a save to make.

Image source, SNS

St Mirren have the lead and deservedly so.

Hearts have not competed in the first half, the best example of which was the space afforded to Alex Gogic as he volleyed the hosts in front.

It's only one-nil, though and this tie could yet go either way.

Image source, SNS