Leinster leave the door ajar
Castres 24 Leinster 24
Leinster will have to wait until tomorrow to ensure they have a home quarter-final, but barring a miraculous Connacht win an hour down the road in Toulouse, they will be back in Dublin in April.
The squad made the province's bean-counters sweat with a nervily secured draw as they repelled Castres' late drive for their line and were grateful for the French side's decision not to kick a penalty to win it as they got the two points they needed due to Dan Leavy's try and Ross Byrne's conversion.
Leinster No 8 Jamie Heaslip wasn't happy with the standard of their performance, despite being guaranteed a place in the knockouts after last year failing to make the grade
"We wanted to go out there and ensure we could get a home-quarter-final, but we weren't up to our standard," he said.
"We didn't play to the best and we gave Castres an opportunity to get into the game. They're a good side and they took it.
"We turned over the ball a few times, we weren't accurate in our rucks but we showed great heart to come back into the game at the very end."
The Stade Pierre Antoine is renowned for being one of European rugby's more hostile venues, but when Leinster emerged to a more than half-empty stadium, they may have felt that their battle was already half-won.
The home side had other ideas and with Johnny Sexton and Isa Nacewa forced off with first-half injuries, they caused Leo Cullen's side the type of problems they haven't encountered for some time. The Blues lacked the accuracy of previous weeks, but showed grit to get their way.
Leinster got the scoreboard moving through a Sexton penalty and the floodgates threatened minutes later. Julien Caminati dropped the ball in mid-field. Garry Ringrose capitalised, picking up and popping the ball up for his centre partner Robbie Henshaw and, while Caminati got a hand in, the former Connacht man re-gathered and out-ran Julien Dumora to score.
Sexton converted but Leinster were soon out of their comfort zone as Castres grew into the game and while Adam Byrne tackled Afusipa Taumoepeau into touch and Devin Toner picked off a key lineout after the hosts had eschewed a kick at goal, the hosts were growing in confidence.
But the pressure told when scrum-half Antoine Dupont took advantage of a Toner slip to go over untouched after Sexton had slipped off an attempted big hit on Pierre Berard. Dumora narrowed the gap to three with the conversion.
Rory O'Loughlin thought he had restored Leinster's lead after Ross Byrne chipped through but his score was ruled out by the television match official and referee Greg Garner after Pierre Berard just did enough to put off the winger.
Castres drew level with a penalty after brilliant feet from David Smith saw him scythe through a gap in the Leinster rearguard and Ross Molony was penalised for not rolling away.
Suddenly the locals who had turned up were fully engaged as their team began to cause all sorts of problems in the wide channels.
They went ahead when Florian Vialelle stood Ringrose up for long enough to get an out-the-back pass away to Smith and he scorched the outside defender to score, with Dumora again converting.
With Nacewa joining Sexton in the stands, Leinster were suddenly in trouble and they looked to hit back instantly when slick hands from Ross Byrne released Jack Conan up the middle but with the line beckoning he was caught by the chasing Dupont; from a subsequent scrum in a great attacking position, Dupont nailed Luke McGrath to force a knock-on to preserve Castres' lead to the break.
Although Castres brought on their first-choice props on the resumption, Leinster started the second half well.
Another opportunity went a-begging in the moments after the restart when another brilliant piece of Ringrose play saw him glide through the home defence, but he couldn't connect with McGrath with the killer pass.
They didn't have to wait too much longer to level as a Castres knock-on allowed Leinster to attack off a scrum and Adam Byrne stepped outside Berard's tackle and he drew Florian Vialelle's tackle before off-loading for Henshaw to score.
Ross Byrne levelled with the conversion and things might have gotten even better had McGrath not displayed another case of butter-fingers, allowing Rob Kearney's pass to slip through his grip after the replacement full-back made a break from the kick-off.
That error was compounded when, with his first touch, James Tracy was penalised for a crooked throw and the subsequent scrum was penalised for a collapse.
Castres took full advantage of the field position, forcing some heroic defending from Adam Byrne, McGrath and Tracy before the pressure told when Smith crashed over from close-range and Dumora restored the seven-point lead.
A big play from Conan turned the momentum Leinster's way once more, but again their inaccuracy cost them as Rory O'Loughlin knocked on before a crucial five-metre Tracy throw sailed over everyone.
Still, Leinster came and after more excellent work from Adam Byrne and Conan, Berard was sent to the sin-bin for not rolling away on his own line as Leinster looked to score.
Leinster went for the scrum and within three phases Dan Leavy forced his way over and Byrne levelled with the pressure kick.
After absorbing more pressure, Leinster almost broke free on the counter as Adam Byrne kicked ahead but the bounce evaded Kearney and Vialelle did brilliantly to dispossess Ringrose when he gathered the ball.
Instead, it was the hosts who went for the win, thrice turning down kickeable penalties as Mike McCarthy was sent to the sin-bin seconds after coming on.
Leinster managed to hold up a driving maul to force a scrum and despite being down a man they managed to force a penalty that allowed Ross Byrne to relieve the pressure. They secured the lineout and Jamison Gibson Park put the ball in the stand. Job done, just about.
CASTRES - P Berard; J Caminati, A Taumoepeau (T Combezou 37-40, 70), F Vialelle, D Smith; J Dumora (B Urdapilleta 63), A Dupont (J Seron 62) ; A Tichit (M Lazar h-t), B Mach (D Tussac h-t), D Kotze (J Jenneker h-t); V Moreaux (L Jacquet 18-24, 70), R Capo Ortega (capt); Y Caballero, A Bias (A Jelonch 62), S Mafi.
LEINSTER - I Nacewa (capt, R Kearney 22); A Byrne, G Ringrose, R Henshaw, R O'Loughlin; J Sexton (R Byrne 22), L McGrath (J Gibson-Park 61); C Healy (J McGrath 48), R Strauss (J Tracy 48), T Furlong (M Bent 73); R Molony (M McCarthy 76), D Toner; J Conan, J van der Flier (D Leavy 61), J Heaslip.
Ref - G Garner (RFU)