Ashley Young starred as his double either side of Stewart Downing's strike and a Grant Hanley earned Villa the points.
"We set up to try and nullify Villa through the middle of the pitch by playing three in there," said Kean. "We were excellent in the early part and trying to get a clean sheet as a platform.
"Villa started to get on top just before half-time and I felt we were getting a little bit deep. We said it was important to keep it tight for the first 15 minutes of the second half and then hopefully the crowd would get restless.
"Before the penalty we had a great chance ourselves and Brad Friedel made a good save and a minute later we are a goal down.
"It is a bad day after that. We found ourselves chasing the game and being a little bit open."