Roberto Martinez accused Everton of wasting the first half against Manchester United in Saturday's 3-0 defeat at Goodison Park.
Two goals in four minutes from Morgan Schneiderlin and Ander Herrera put United in control before the break, with Wayne Rooney adding a decisive third just past the hour mark.
Martinez was frustrated with the way his side reacted to going a goal behind and has called for a quick reaction when Everton visit Arsenal next Saturday.
"It was very uncharacteristic. We started quite slow, it looked like a group of players coming back from internationals," he said afterwards.
"We conceded a goal, [from] a dead-ball situation, and it affected us too much. We wasted the first half from then onwards. We were very slow, couldn't see a forward pass, became negative.
"We reset at half-time, we started playing as our normal selves and I felt it could've been a very different game had we scored at that moment.
"But with one mistake, one chance on the counter-attack, Man United took advantage and we got deflated again, the game went away from us.
"It's something we need to put right and react quickly for the next game."
A minute's applause was held prior to kick-off to honour former Everton boss Howard Kendall, who died at the age of 69 earlier on Saturday.
Martinez does not believe Everton's performance was affected by the news and was keen to pay tribute to the man who won the First Division title as both a player and a manger on Merseyside.
"I think it was shocking news. You can imagine pre-match it was really really sad. We wanted to change it round and make it a celebration - I think Howard would've wanted that," Martinez added.
"He was an iconic footballer, he'll always be an inspiration for any manager with the privilege to manage our football club. He deserves an incredible amount of respect and a big thank you for putting Everton at the level he did.
"I want to believe that never affected us at the start of the game."
