O'Connell: I was embarrassed
The former British and Irish Lions captain was making his final test appearance in Dublin before he retires from international rugby after the World Cup.
"There are a certain amount of things we wanted to improve on from and we didn't do that," O'Connell told AFP. "From our point of view, that is disappointing.
"There are certain things we pride ourselves on and we didn’t do a whole lot of those very well, with discipline being one of them.
"The penalty count is a big thing. Wales are a big side, and we gave them a few good cracks at us on five-metre drives, and we gave Leigh Halfpenny a lot of kicks at goal."
O'Connell said the result was not the way he wanted to say goodbye to the home crowd.
"It's very hard to play as well as you would like in your first start of the season. I really appreciated the reception I got from the crowd. I was embarrassed that we lost the game."
Wales led 10-0 inside 26 minutes after two kicks from Halfpenny either side of a push-over try by the combined weight of the Welsh forwards and backs, finished by man-of-the-match Justin Tipuric.
Ireland levelled on the stroke of half-time through Jonathan Sexton and a powerful score from lock Iain Henderson.
But two Halfpenny penalties capped a fine Welsh performance that will go some way to deciding the make-up of Gatland’s final 31-man squad, to be named on Monday. Wales then welcome Italy to Cardiff next weekend for their last warm-up fixture.
"We had about 25 or 26 players nailed-down and now we will sit down as a group and make those tough last few decisions," said Gatland.
Ireland play their final World Cup warm-up match against England at Twickenham next Saturday (September 5) and will clearly require an improved display if they are to live up to their billing as genuine contenders for the Webb Ellis trophy.
Agence France-Presse