He was furious after watching his team fail to turn first-half domination into goals and then hand victory to Reading with defensive errors.
Moyes said: "I am not happy that they are not winning those games. If we realistically want the opportunity to mix it with the top teams then we can't lose games like that.
"We will have games in which we'll play badly, not win and have to take it.
"But we have to win games when we are on top."