Jason Harries was bitterly disappointed to let a 15-point lead slip as he bagged a brace of tries "in vain" on his competitive debut.
Cardiff Blues were cruising and led 29-14 against Leinster after 55 minutes at Cardiff Arms Park with both Harries and Rey Lee-Lo crossing twice.
But the Dubliners displayed their champion quality and snatched a last-gasp defeat after grinding their way back into the game.
Harries said: “Considering where we were in that game around the 55-60 minute period, 15-points up and we have let them back in so it is a tough one to take.
“We’re obviously disappointed because we should have done enough to win. It was a mixture of things, we can’t keep giving penalties away against Leinster because once they get in the 22 they stay there and they score more often than not. That’s just one area we can look at to improve.
“I’m happy to score two tries but ultimately it is all in vain because we haven’t won the game.
“But it was great to see so many people out there tonight supporting us, especially after the heroics of the end of last season with the European Challenge Cup, that’s definitely transferred into the season and getting that crowd here.
“It’s definitely nice running out to that. It was nice to score two on my debut for the Blues here in front of a big crowd and hopefully that can continue.”
Cardiff Blues travel to Italy next with back to back games against Treviso and then Zebre and Harries insists his side can go there with plenty of confidence despite their heartbreak.
He added: “We will learn from it going into next week going to Italy. We have to play for the full 80 because teams like Leinster will keep coming back and they’ve done that tonight.
“In parts of that game we were unstoppable it’s just keeping hold of the ball and going through as many phases as possible because when we do we break teams down and score tries. Moving forward that’s an area we can really target and improve on.”
Wales’ Capital Region return to the Arms Park on Friday, September 21, when they face Munster. Tickets are available now by calling 029 20 302030 or clicking here.