Ospreys captain Alun Wyn Jones says they had "no excuses" for the "wake-up call" provided by their first Pro12 defeat of the season, against Leinster.
Having hammered Zebre, Connacht and Treviso, the Welsh region were beaten 31-19 in Dublin.
"No excuses. We've gone well in the first three games, but realise who we were up against and it's a wake-up call," said the Wales lock.
Head coach Steve Tandy said indiscipline cost his side.
After losing on his 200th Ospreys appearance, Jones said: "It was going to come sooner or later, I suppose, but we've got a lot to work on moving forward."
Ospreys fought back after trailing 24-0 the break with Ben John, Dafydd Howells and James King scoring tries.
"Too little, too late," was Jones' verdict.
He added: "We needed to keep the ball and not be so over-enthusiastic at the breakdown and give away penalties.
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"We began the second half in that fashion. We came out saying 'not to make penalties'.
"And the first thing we do is give them an easy shot goal and put ourselves under pressure."
Tandy underlined Ospreys failings, saying: "We were indisciplined.
"We gave too many cheap penalties away, cheap turnovers and coming to the RDS with a strong Leinster team, you're not going to recover.
"And I don't think it was lack of effort when we were defending, it's just that we were continually inviting Leinster into our half and into our 22."
Tandy said prop Dmitri Arhip's sin-binning for a high tackle in the 27th minute "had an effect", but "the damage was done before that".
"It was a bit harsh as a yellow, but ultimately we've given too many penalties away," said the ex-Ospreys flanker.
"Probably on reflection we got what we deserved, which is nothing out of the game."