Colin Gregor
Former Glasgow Warriors back on BBC Radio Scotland

It's so loose, the number of turnovers we've had, it's one turnover into another turnover.

It's an incredibly loose opening, here. Virtually structure-less.

A fabulous turnover from Josh Macleod gets Scarlets some long-awaited front-foot ball.

Sam Costelow blasts a crossfield bomb which Kyle Steyn catches outside his 22.

Glasgow lose the ball by dint of a stray boot at the breakdown, then wrestle it back and boot it long.

Scarlets come again on the counter, but Sam Lousi's back-door off-load whizzes into touch.

Lungs will be rasping already here...

Peter Wright
Former Scotland prop on BBC Radio Scotland

There's almost been no pattern to the attack.

Glasgow have almost been playing sevens and Scarlets the same. The way the conditions are, it's got the makings of an absolute classic.

There's no mauling opportunity as the line-out throw slips beyond the fingertips of JP du Preez.

Zander Fagerson gobbles it up, and Glasgow spin it wide, but Ollie Smith and Sebastian Cancelliere rather get in each other's way.

Penalty Scarlets for the fairly blatant obstruction.

That's a big release for the home side, who have hardly touched the ball so far.

Image source, Huw Evans Picture Agency

Gareth Griffiths
BBC Sport Wales at Parc y Scarlets

Centre Johnny Williams being forced off the field after suffering a head injury is a big blow for the Scarlets.

Williams has been integral to the Scarlets' renaissance this season and has forced a reshuffle in the home midfield.

Scarlets will miss his power and pace if he does not return from his head injury assessment (HIA).

The Glasgow back-row trident of Rory Darge, Sione Vailanu and Jack Dempsey are punching painful holes in the Scarlets defence.

George Horne is scragged from an offside position and the Scarlets penalty count grows to four inside the opening 10 minutes.

From inside the 22, Kyle Steyn points to the touchline. They'll throw in to the line-out five metres out...

Another Scarlets penalty - this one for offside - and another Scarlets injury.

Johnny Williams rushes up to hit Sione Tuipulotu but gets his head on the wrong side of the beefy centre.

If Williams is showing clear concussion symptoms - which certainly seems the case - he will play no further part in this game.

Ioan Nicholas comes on.

Dwayne Peel's resources stretched already.

Colin Gregor
Former Glasgow Warriors back on BBC Radio Scotland

Jack Dempsey's big barge through the middle got Glasgow on the front foot, then Tuipulotu comes with his distribution abilities and a great finish from McDowall.

Scotland international Javan Sebastian was injured in the lead-up to the McDowall try.

Sam Wainwright has come on for the tight-head prop.

Glasgow, meanwhile, win a scrum penalty at the first set-piece of the match and clear downfield.

Okay, this is already verging on the bonkers.

Straight from the restart, Vaea Fifita extends a huge Tongan arm into the air and pilfers it back for Scarlets.

He links acrobatically with compatriot Sam Lousi, who strides into the 22 and has the ball waving above his head, looking for an off-load.

Jack Dempsey steals it back, and Glasgow wind up with a scrum.

Confident opening from Glasgow, who get into their attacking shape early with big carries from Sione Tuipulotu and Kyle Steyn on either flank. Then Jack Dempsey veers infield and carves his way up to the Scarlets 22.

They attack the home red zone with a penalty advantage up their sleeve.

Off we go! Scarlets kick off and the first Challenge Cup semi-final is under way.

Parc y Scarlets really does look fabulous, the sun beaming down, and the stadium packed out with great swathes of red.

The teams emerge to a mighty roar.

Image source, Huw Evans Picture Agency

Scarlets head coach Dwayne Peel tells BT Sport: "A semi-final is always a tricky one, but we have to go out and try and win the game, not to protect anything.

"Being at home doesn’t win you anything. We have to be bold. That’s the message we have delivered.

"Especially with younger guys, some haven't been in this position before, so it’s a great opportunity for them."

Image source, SNS

Glasgow head coach Franco Smith tells BT Sport: "Unfortunately Richie Gray didn’t present well yesterday before we travelled which is a pity but with next week [Glasgow play Munster in the URC play-offs] in mind, it wasn’t worthwhile risking anything. We made the change straight away yesterday afternoon.

"We are absolutely focused, we will take it one game at a time. It’s an old sports saying and it is very relevant to these circumstances.

"It’s about managing the players and recovery next week. It’s important for us to learn how to play away from home in these conditions and with games of this importance."

Chris Horsman
Former Wales coach on BBC Radio Wales

Glasgow have only lost once in 17 games.

Scarlets have lost their last two games and I think those losses are just going to tip the balance in Glasgow's favour.

Image source, Huw Evans Picture Agency

Scarlets number eight Vaea Fifita is effectively a rugby cheat code.

For various salary cap-related reasons we won't go into right now, Wasps couldn't keep the towering All Black last season, and the Scarlets were only too happy to snap him up.

What a move it's been.

Fifita is faster than some international centres and has better hands than some international fly-halves. Oh, and he's 6ft 6ins.

He has been involved in some utterly breathtaking attacking moments, including some wonderful tries of his own, and is a massive X-factor threat.

Image source, SNS

Ryan Wilson has been a Glasgow Warrior for 13 years and most people who have played or worked for the club will tell you he is the heart and soul of Scotstoun.

Approaching his 34th birthday, Wilson was recently informed he would not be offered a new deal beyond the end of the season. He hopes to continue playing, but we don't know if he's managed to secure a new club yet in this tough recruitment market.

The back-row was given a home send-off - ironically, against Scarlets - a fortnight ago, and was a travelling reserve for today's fixture.

With Richie Gray pulling out, he's now on the bench.

There are shades of Wilson's 50th, and final, Scotland cap in 2021, when he ended a long spell in the international wilderness to play a part in his country's first win in France since 1999.

Glasgow have scored the most tries (31) and points (211) in this year's Challenge Cup, averaging just over five tries per match.

Scarlets, though, have made more running metres and line breaks than any other side.

But Glasgow, who are second in both those categories, are top for defenders beaten.

Basically, this should be a try-fest.