There were two tries apiece for home star David Smith and Leinster’s Irish centre Robbie Henshaw as the visitors discovered just how hard it is to win at Stade Pierre Antoine. Castres may have been out of the running for a place in the last eight, but they put up a huge fight.

In the end, it took a magnificent rearguard effort from pool winners Leinster, who were reduced to 14 men for the final four minutes when Mike McCarthy went to the sin-bin, to hold on for the draw and two vital points. They now have to wait to see if Connacht can get the full five points in Toulouse to challenge them for a home draw.

Leinster went out of the blocks at breakneck speed and were 10 points ahead in as many minutes thanks to an early Johnny Sexton penalty and hen conversion of the first of Henshaw’s tries. But then the Irish playmaker limped out of the battle midway through the first half  – they also lost sipper Isa Nacewa later on – to be replaced by Ross Byrne.

Just before Sexton left, Castres hit back with a try by scrum half Antoine Dupont and was converted by Julien Dumora to cut the gap to three points. Dumora then levelled things up on the half-hour before Smith struck with the first of his tries on the end of a sweet back line passing move for a try that Dumora converted to make it 17-10 at the break.

It seemed as though Leinster had steadied the ship two minutes into the second half when Adam Byrne came off his wing to act as first receiver from a scrum in the home 22 and make the break that allowed Henshaw to cross at the posts for his second try.

Ross Byrne’s conversion drew Leinster level, but they made too many mistakes, and snubbed too many chances, to build on that great start to the second half. They did tighten up on the defence – they missed 17 tackles in the first-half –but couldn’t stop Smith scoring his second try at the foot of the right hand upright for a try that Dumora improved to make it 24-17 to the home side.

Leinster got a chance to strike when Pierre Berard was sent to the sin-bin on 62 minutes. A minute later, replacement back row man Dan Leavy barged his way over from close range and Ross Byrne converted to level the scores again.

But it was Castres, who grew stronger as the game went on as they introduced more of their front line players, who finished the stronger and put Leinster under intense pressure. They held out in the end and will now have to sit and wait to see if they get a home draw.