Midfield pair Casemiro and Kobbie Mainoo were both at fault for the three goals United conceded.
"We started the game really well and got more chances," Fernandes told Sky Sports afterwards. "We have to be more clinical, this happened against Fulham too. They were clinical.
"I don't look at the stats but the game was tight.
"We don't need to be pointing fingers at everyone, that won't help us now.
"What's the point in saying Casemiro lost the ball or Kobbie lost the ball? They lost the ball because they wanted to be brave. It's part of football. Don't make it individual.
"Casemiro is more experienced than me. I don't need to tell him anything, he knows what football is about. He's played for the two best clubs in the world.
"Kobbie is an excellent kid. I want him to try more and do this because it's part of his game. They are huge players for us and will keep being."