There's a lot of head shaking on the sidelines from Leone Nakarawa. His yellow card seemed harsh and he would have been right where Saints scored that follow-up try.

Leone Nakarawa is in the bin and...

Will Saints' bold approach pay off? They wheel left from the lineout, twice they go close to breaking through and then there is another penalty given. And has warned...

Castres give up another penalty and Fin Smith kicks into the corner instead of taking the three points. They want more.

The referee is losing patience with the front row of Castres as they collapse another scrum.

Mantej Mann
BBC Sport at Franklin's Gardens

Each time the incident between Josh Kemeny and Remy Baget was replayed on the big screen, the groans from the home crowd got louder.

In the end, Saints and their fans will have to settle for the three points from the boot of Fin Smith.

Castres having their best spell now, and are held up close to the line. Did that go over in fact?

'The next one goes to the bin', referee Andre Piardi warns Castres as Fin Smith slots over the penalty.

The television pundits and the home fans are a bit befuddled by that call. I think Castres can consider themselves fortunate there.

Still, here come Saints once more.

A lot to clear up. It's no try and the referee says there is no yellow card for that head on head shot.

No penalty try either.

It's just a penalty.

Lots going on here. Josh Kemeny almost dropped the ball but recovered it, his foot was then in touch and he was hit in the head by Castres wing Remy Baget.

Josh Lemeny was put in wide on the right after more great midfield play from George Furbank, but the flanker may have lost the ball before he grounded it.

Is that another try for Saints?!

Alex Mitchell is inches away from touching a loose ball down on the tryline but he can't gather in and Leone Nakarawa does a great job of clearing his lines for Castres.

Image source, PA Media

When Northampton have all of their players available and they play like this they are some side to watch. Hard to believe that they are only eighth in the Premiership.

It's number eight Abraham Papalii who needed patching up. We are back playing.

'There's a lot of blood in your mouth', says referee Andrea Piardi. Some running repairs needed in the Castres forward line.

This has been a super impressive opening from Saints. A reminder though that the winner of this one will face Leinster in the last four.