Watford head coach Gianfranco Zola admitted he had failed to do his homework after his team were thrashed 5-1 by Derby at Pride Park.
The Hornets were stung by three set-pieces as Derby exploited awful defending to romp to their first victory of the season and Zola took the blame.
"I apologised to the players because I underestimated the value of this team at set-plays," he said.
"I said to them 'it's my fault'. There are not many positives to say about this because the result is big and it's been a poor performance."
Zola accepted the sale of centre-half Martin Taylor to Sheffield Wednesday had not helped, but added: "The rest of the team must take responsibility and do better and that's everybody, including myself.
"I should have been more aware of the dangers of the opposition.
"We started okay but it was a poor reaction to the first goal, we just kind of stopped playing. They deserved to win but this is the Championship and if you give away cheap goals like we did for the first two then you are in trouble and that's what happened to us.
Derby coach Andy Garner was delighted with the team display and the performance of striker Conor Sammon, who scored his first goal for the club. Richard Keogh, Jeff Hendrick, Will Hughes and Jamie Ward were also on target for the Rams
Garner said: "We are a little bit disappointed we conceded a goal but we are not going to say too much about that to the players after the effort and performance they've put in. Nothing takes away from the result and what the players have done.
"We were disappointed at Wolves last week. You could see the players were disappointed not to get all three points after that performance and they carried that on in training this week and carried it on in this game. Conor was absolutely brilliant. I fancied him to score and I said that to him in the warm-up and he thought he would score as well."