Nope, this time it's the Scarlets who falter at the line-out.

Glasgow have possession, and Zander Fagerson embarks on a colossal ball-carry which sends Morgan Jones sprawling.

The officials seem to agree that one falls into the 'rugby incident' category.

There is no separation between Fagerson's arm and his body, which is what the referees check for these days.

Gareth Delve
Former Wales international on BBC Radio Wales

They're just winning these moments.

Scarlets are getting everything right just as Glasgow are getting everything wrong.

There's a lot of self-harm about the past few minutes for Glasgow. Line-out shaky, discipline wavering, and some rather hair-brained decisions in tight spots.

Scarlets are feasting on those errors and boy, the crowd are loving it

Another breakdown penalty for the hosts as Ollie Smith is swallowed up by red-shirted chasers.

Guess who? Josh Macleod again! Brilliant from the flanker.

Scarlets kick to the Glasgow 22 once more.

Five minutes of the half left.

Gareth Delve
Former Wales international on BBC Radio Wales

Superb hands from Johnny McNicholl, the take and give all in one motion and a superbly floated pass for Steff Evans to canter over.

Wait a second.

Television pictures have confirmed Steff Evans' boot grazed the touchline just before he flung the ball inside.

Glasgow line-out, not Scarlets scrum.

THIS. IS. BONKERS.

JP du Preez looses the ball forwards in the middle, Sam Lousi scoops up and swings a telescopic right leg at it.

The ball is comfortably fielded by Ollie Smith, but his pass to Kyle Steyn is wild, putting the captain under massive pressure.

Steyn loses it, Steff Evans gathers and hares towards the corner, but his inside ball is knocked backwards off a Glasgow hand and smothered by Ollie Smith.

The upshot? Scrum-five, Scarlets put-in.

What a chance...

Image source, PA Media

Peter Wright
Former Scotland prop on BBC Radio Scotland

Reynal at his best, he’s petty.

Nobody ever gets penalised for that - he asked Kyle Steyn for his 'players to respect the offside line'.

I've never seen it yet!

Two from two for Sam Costelow.

It's a one-point game.

'Sur la tete?', asks our referee Mathieu Raynal.

A hanging George Horne box kick does indeed strike the bonce of Sam Costelow. Summing up the madcap nature of this game.

Glasgow concede an offside penalty, and the Scarlets ask Costelow to go for the posts once more.

The momentum has shifted significantly in favour of the West Walians.

Colin Gregor
Former Glasgow Warriors back on BBC Radio Scotland

Smart play from the Scarlets.

They pinned Du Preez into the ruck, he's trying to roll but he can't.

Mathieu Reynal can't see that and penalises the Warriors second-row.

Official stats show Scarlets have only had 23% possession so far!

Image source, Huw Evans Picture Agency

Sam Costelow, whose brilliant late kick sunk Clermont in the quarter-finals, lines up his first kick of the evening.

It's about 30m out, slightly right of centre...

And the young Welshman nails it.

Scarlets on the board, and beginning to find their groove.

Peter Wright
Former Scotland prop on BBC Radio Scotland

The scrappiness is making it really exciting.

There's so many errors and both teams are really good on the counter attack, but making those errors later in the game is going to have a real effect.

After Ollie Smith's sliced clearance, the Scarlets reload and launch again.

This time, they whip wide to the left, but Ryan Conbeer is shackled by Sebastian Cancelliere.

Scarlets aren't done yet, though, as they pilfer the Warriors line-out and barrel into the away 22 once more.

The crowd is beginning to grow in confidence and anticipation.

The hosts win a penalty, and will go for goal.

Now the Scarlets have an attacking foothold from that Macleod turnover.

They come surging towards the Glasgow 22, Gareth Davies with a superb snipe and sprint around the breakdown, sitting hooker George Turner on his haunches and handing on to Joe Roberts.

The centre can't quite cling on under heavy Glasgow pressure, and Warriors will put in at the scrum just inside their own 22.

Gareth Delve
Former Wales international on BBC Radio Wales

Looking across the Glasgow backline, they are just massive.

McDowall, Tuipulotu, Steyn - with that triple threat they're just finding a couple of edges.

Glasgow have the edge at scrum time, but Scarlets are winning the breakdown battle.

Josh Macleod has burgled two Glasgow rucks now.

It's a hugely compelling battle between the jackals, Macleod and Darge.

Semi-finals can often be cagey affairs. You know the kind of game we mean - nobody wanting to make an error, a reluctance to give the ball air or push the envelope.

That is precisely the opposite of what we're seeing here.

Some of the rugby on show is mad. Off-loads galore, knock-ons everywhere, absolutely no discernible shape, heaps of enterprise.

Peter Wright
Former Scotland prop on BBC Radio Scotland

Scarlets have already missed 15 tackles, Glasgow have missed none.