Manchester City boss Roberto Mancini said he was guilty of not preparing his team properly after they slipped to a 1-0 defeat at Everton.
The Premier League leaders remain top on goal difference after Darron Gibson scored the only goal, while Manchester United beat Stoke at Old Trafford.
"Probably it's my fault because we didn't prepare very well for this game," Mancini told BBC Sport.
"I thought before the game it was going to be easier but it is never easy."
Mancini later suggested he had made mistakes with the team in training.
"The players put everything on the pitch but I made some mistakes during the last three days preparing for this game," he added.
Ex-Manchester United midfielder Gibson scored in the second half to give his former club an added boost, as the Premier League champions registered a 2-0 victory over Tony Pulis's side to close the gap at the top of the table.
Mancini admitted his team struggled against a side who they have beaten only once in 14 trips to Goodison Park.
"Everton at home is a strong team," he added. "Every time they play against us they play very well.
"This evening we had the chance and when we conceded a goal we didn't have more chances to score."
Other than a couple of Samir Nasri efforts which hit the bar, City were restricted to two penalty appeals, first when Sergio Aguero was brought down and then when Aleksandar Kolarov's cross appeared to strike Phil Neville's arm.
"The decisions are very unlucky against us at this moment," said Mancini, who has also had to do without the suspended Mario Balotelli.
"It's very important that we start to win next Saturday against Fulham. The season is long, we have 15 games [to go] and I hope we can recover all the players quickly.
"But it's important that we recover our strength this week."
Mancini said he hoped new loan signing David Pizarro could help out his team. "He is a good midfielder, he has experience and I know him very well," he said.