Italy shipped 25 points in 40 minutes to sink to their third 2012 RBS 6 Nations loss, yet at half-time the score stood at 17-10.
Italy captain and No. 8 Sergio Parisse's try just before half-time brought the scores level but wing Tommy Bowe replied immediately and Ireland stepped up their game in the second half with another Bowe try and two more late on from replacement lock Tom Court and wing Andrew Trimble.
"In the second half they were stronger," conceded Brunel.
"We lost too many one-on-one duels and in defence we were in a lot of difficulty.
"The guys lost territory and slipped off tackles and, with the speed of the Irish, it became a mission impossible.
"I don't know why it was we suffered so much."
Brunel however refused to point the finger at new fly-half Tobias Botes who had a difficult day from the kicking tee.
A scrum-half for Treviso by trade he missed three kicks at goal in his first international start.
"After the game with the English, there was a lot of attention from the media with criticisms that don't help at all and created difficulty."