Northampton haven't had lots of opportunity to attack since the interval but they win the penalty as Leinster try to play the ball at the breakdown.

Fin Smith lining up a long shot at goal.

Jonathan Bradley
BBC Sport NI Senior Journalist

We've come to expect 50:22s from James Lowe. Not so much from Caelan Doris, it must be said.

The Leinster maul just hasn't got going today, though.

This is the sort of semi-final where those moments feel like such huge swings of momentum.

New Zealand's Jordie Barrett is onto the field for Leinster. The World Cup winner replaces Robbie Henshaw at inside centre.

From try-scorer to deadly kicker.

Caelan Doris rips the ball in the tackle before spinning and firing a 50:22 down the other end.

The Leinster faithful like that but their side then make a hash of the subsequent line-out.

This semi-final is so finely poised.

Caelan Doris makes a slight break but he loses control of the ball as he tries to force the offload.

Sam Prendergast then drops a low pass by Jamison Gibson-Park.

Leinster are masters of their own misfortune at the moment.

You have to wonder how Leinster will respond.

The Irish province were favourites to reach a fourth consecutive Champions Cup final, but it all looks very different now.

Fin Smith gets us back up and running...

Paul Grayson
Former Northampton and England fly-half on BBC Radio 5 Sports Extra

Sensational stuff from Northampton. They've taken every single opportunity presented to them, created by themselves.

Breathtaking counter-attack try for Tommy Freeman first, Fin Smith makes the break and nudges the ball through.

And then the offload for the last Freeman try, Juarno Augustus, one-handed over the top, and Freeman's finish was world class.

It's been the Tommy Freeman show...

Image source, Getty Images

Jonathan Bradley
BBC Sport NI Senior Journalist

With the likes of RG Snyman, Jordie Barrett and Rabah Slimani all added to the squad for this season, and their subsequent dominance of the two knock-out rounds so far, there has been a sense of 'if not now, when?' about Leinster's quest for a first European title since 2018.

Well, after Tommy Freeman's first-half hat-trick, if they are to maintain hopes of getting their hands on the trophy again next month, they're about to face a serious examination of their title credentials.

The Saints have been superb in Dublin!

Leinster are intent on reducing the deficit before the interval but Saints stem the tide and manage to win the penalty.

Fin Smith pops it into touch and that will be that after a thrilling first half.

Don't. Go. Anywhere!

I missed it in the melee after Josh van der Flier's try but Northampton hooker Curtis Langdon was sent to the sin-bin for his role in trying to disrupt the Leinster attack.

I've only realised he was shown a yellow card because he has just returned to the field after serving his 10-minute punishment.

Oh the joys of being a live-texter when it's end-to-end!

Jonathan Bradley
BBC Sport NI Senior Journalist

With a certain squad being announced next week, there's even more focus on the positional match-ups than normal this weekend.

So how about that passage from the two open-side flankers?

Josh van der Flier caps his strong start to this one off with a try but then Pollock shows exactly why he's been making so many headlines of late.

An engrossing half an hour here!

Northampton win the penalty inside the Leinster 22 and Fin Smith bangs it over from the tee.

The visitors regain the lead.

James Burridge
BBC Sport rugby commentator on BBC Radio 5 Sports Extra

This game is exhilirating to watch already