Leinster fly-half Jonathan Sexton admitted his team made too many first-half mistakes to win their Champions Cup semi-final against Clermont Auvergne.
The French side raced to a 15-0 lead inside the opening 20 minutes as Leinster struggled to settle into the game, and despite a furious second-half fightback, Leo Cullen's side fell to a 27-22 defeat in Lyon.
A disappointed Sexton said: "We gave them a head-start and you can't do that in a semi-final.
"We still felt we could have won it at half time, but we were beaten by an impressive side and we have to take our hats off and say we weren't good enough.
"It's a new feeling losing in a European semi-final - I've never that felt that before and it hurts.
"We've got a young squad and only a couple of old heads left like Isa (Nacewa) and me. We don't have many more days left and we've got to urge these young players to not think that they've got loads of chances at it - you have got to take every one like it's your last one."
Leinster battled back gamely early in the second half and appeared to take the lead when Dan Leavy stretched for the line to finish a fine flowing move.
But the television match official alerted referee Nigel Owens to a possible offence by Leinster and replays showed Leavy himself guilty of holding onto Aurelien Rougerie at a ruck and preventing the Clermont man making a tackle.
"He tackled him in the ruck and maybe he held him a bit too long," Sexton acknowledged. "Was he going to make the tackle? I'm not sure, but we can't complain about the calls."
David Strettle played a key part in Clermont's early dominance in defence and attack and scored Les Jaunards second try to help book a final berth against his former club, Saracens, in next month's final at Murrayfield.
The England wing, though, was full of praise for out-half Camille Lopez, who remained calm in the face of the Leinster onslaught to kick a penalty and two late drop goals to see Clermont home.
"We knew Leinster wouldn't give up," Strettle said.
"We said we had to start well in front of this remarkable crowd and we did that. But we knew they would have a purple patch and they did.
"In Camille we have got a player who can control the game. Now we have to go and do it all over again in the final. You can see how good a team Saracens are.
"It is going to take a hell of a job to beat them."
