Leinster coach Michael Cheika breathed a huge sigh of relief after the Heineken Cup holders squeezed past Clermont Auvergne 29-28 to book their place in the last four.
Two tries from Ireland No. 8 Jamie Heaslip and 19 points from the boot of fly-half Jonathan Sexton edged Leinster through.
Clermont fly-half Brock James fluffed a last-gasp drop goal to snatch the win and Cheika admitted his side had got lucky.
“When the players came into the dressing room after the game they weren’t in a celebratory mood because they realised their ill-discipline could have cost them a semi final place,” said Cheika.
“We just hung in there and tried to edge back in front. It was very similar to last year against Harlequins.
“With the ball in hand we played well but our discipline simply wasn’t good enough.
“We have to face up to the fact that that kind of discipline won’t be good enough to win the Heineken Cup again.”