Ireland led by 20 points at the break, before the home side reduced their advantage to eight in the second half.
The interim coach told BBC Sport: "We didn't start well, you need a foothold in the game. You can't give any international side the space and time on the ball which we gave in the first 20 minutes.
"It was a game of contrasting halves; I thought the first 20 minutes was key in terms of a couple of turnovers, they dominated both territory and possession and obviously they took their chances.
"It's just making that right decision under pressure. We talked all week about starting well and we didn't start well and as a result Ireland put points on the scoreboard early."
The loss ensures that Wales will not be able to repeat their Grand Slam win from last year.