After watching his side lose 15-12 to Clermont Auvergne, Leinster head coach Joe Schmidt was frustrated that they did not get more than a losing bonus point out of the game.
Trailing by six points at half-time after Morgan Parra's four penalties and a Brock James drop goal put the home side in front, Jonathan Sexton's fourth penalty brought Leinster within touching distance of victory.
But despite being held scoreless in the second half, Clermont hung on to stretch their unbeaten home run to 51 games and move five points clear of the defending European champions at the top of Pool 5.
Schmidt says it will be difficult to lift his team after their impressive second-half comeback came up short.
With the sides meeting again in Dublin next Saturday, he reflected: "It is incredibly disappointing. The fact that we've got to try to get ourselves up and forge ahead for next week is going to be tough as well. We've got a fair few bruised bodies in there."
Leinster fly-half Sexton turned down the chance to go for a penalty early in the second half and opted to try to pick out Fergus McFadden with an ambitious cross-field kick, but Schmidt said that showed how much his side wanted to win the match.
"I just think you come to the (Stade) Marcel Michelin and I think you've got to get over the line. You can't just go between the posts and hope to get something here," added the New Zealander.
"I thought there were a couple of calls that maybe could have gone our way and we could have got something else between the posts.
"But the area that Johnny actually kicked out of when he cross-kicked was very, very heavy and muddy. It's not a guaranteed three. We did miss one and they didn't miss any. So that's how close these games are and it is really unfortunate."
"We've got a fair few bruised bodies in there" - Joe Schmidt
Having gone into the game two points ahead of Leinster, Clermont boss Vern Cotter was relieved to see his side cling on for their third win of the pool stages.
"We weren't particularly good in the second half and they were better in the second half than they were in the first half. We just did enough to stay ahead," he said.
"The game was contested from start to finish very intensely, especially at the breakdown. They threw everything at us and I'm pleased that we managed to sneak away with the victory. Even if it was a skinny one, it was still four points and I think that will count in the end."
The stage is set for a thrilling rematch at the Aviva Stadium next Saturday afternoon, but Cotter said it is dangerous to think that the round four fixture will decide who comes through the pool.
"The biggest mistake is to think there's only Leinster in the pool. These back-to-back confrontations determine the outcome most of the time.
"But this is going to be open and we need to see what happens in six days really. That's probably when both teams will know where they stand," added Cotter.