Ruben Amorim said his Manchester United players abandoned their attacking principles after taking the lead against Fulham, claiming their defensive mentality cost them victory in Sunday's 1-1 Premier League draw at Craven Cottage.
United scored through an own goal off Rodrigo Muniz's back but surrendered their advantage when Fulham substitute Emile Smith Rowe struck 93 seconds after entering the fray.
The result leaves the visitors with a solitary point from their opening two Premier League matches.
"We scored the goal and then we forgot about how we play. We want to win so badly and that is a good feeling, that we scored a goal and everyone on the pitch was thinking, 'Let's hold onto the advantage and try to win the game'," Amorim told the BBC.
"For me that is the moment that we have to enjoy more and push the opponent. We tried to press the opponent super high and left a lot of space.
"We have to grow up a lot as a team. For me the most important thing is that during the week they were working really hard. Today we worked really hard and we are going to improve. The moment that changed the game was our goal."
A pivotal moment in the first half saw United skipper Bruno Fernandes miss a penalty that was awarded after a VAR check, with the playmaker sending it high over the bar.
It marked the fifth time he has missed a penalty since his Premier League debut in 2020.
"I think he is not used to missing penalties. He knows the importance, that this moment can have a huge impact on the team," Amorim told Sky Sports.
"During the game he was not happy because he was not involved and he has so much responsibility and I think he thought missing the penalty was huge for us."
Despite already trailing leaders Arsenal by five points early in the campaign, Amorim remained bullish about United's prospects in the league.
"We just want to win games. The players know they are playing in a club where they need to be better," he said.
"I am really confident that we are going to get many wins."