A dressing-down at half-time was the catalyst for Everton's 3-0 Premier League victory over Sunderland, according to manager Ronald Koeman.
An 11-minute hat-trick from Romelu Lukaku secured three points for the visitors at the Stadium of Light and moved them into third place in the Premier League table.
Lukaku was an isolated figure for much of an end-to-end first half, while Jermain Defoe missed a clear chance to give Sunderland the lead before David Moyes' side collapsed in the second period.
And Koeman, whose decision to take off the ineffective Ross Barkley for Gerard Deulofeu paid dividends when the Spaniard helped set up the first goal, admitted that he made his feelings about the first 45 minutes quite clear to his players.
"I was really disappointed with our first 45 minutes. It wasn't the Everton I like to see. We lost a lot of easy balls, too many players were not on our level in possession," he told Sky Sports.
"But the second half was what I like to see. We had good football, good pressing, we had opportunities to score more goals.
"I told the players I was really angry. We had good defending, but the midfield lost too many balls. Then sometimes you need to make hard decisions at half-time and hope for a good reaction, and that happened in the second half.
"I know my players and the level they can show. That was the level in the second half."
Koeman insists he never doubted that Lukaku would overcome his goalscoring drought and praised the "unbelievable" potential of the 23-year-old.
"I did not have doubts. The two goals with Belgium gave him a boost and it's unbelievable how good he can be," he said.
"Strikers look to score goals and there's always a little doubt in his mind about a long time without scoring for Everton. But I told him that the best answer is always on the pitch, and he showed his qualities."
Koeman also reserved special praise for Idrissa Gueye, who set up Lukaku's opener with a clever cross to cap an authoritative performance in midfield.
"Fantastic," he said of the former Aston Villa man. "Maybe he was the key tonight. He's that player with a lot of energy, and he's quiet on the ball, takes good position. He's a key player, a great signing for us."
Koeman went on to back his players to sustain a fight for the European spots this season - provided that they do not repeat Monday's first-half showing.
"I think we'll be one of the teams who fight for European football. If we play like the first half then we'll be in 13th, 14th place, but we need to fight for Europe," he added.
"The players are not stupid - they know how they can perform. That's what we saw in the second half."