United came into the clash at Villa Park on the back of nine matches unbeaten, form that put them within touching distance of the top four, but after conceding two goals inside five minutes on Sunday, they never looked like extending that run.
Jacob Ramsey's own goal got United back into the game just before half time, but the same player made amends early in the second period, putting the game to bed with a well-taken third goal for Villa, as United slumped to defeat.
"When you start a game like this, you get beat," Ten Hag said. "The details take everything from us, because we didn't press. Today we weren't on it from the start, especially at the start of the game and we lost our balance.
"We didn't follow the rules defending, and we lost our battles. The players on the pitch have to win the game and if they do their jobs 100 percent, with passion and desire, following the rules and principles of football then we win this game."
The Dutchman was particularly critical of his team's tactics in the second half as they tried to get back into the match, saying they went long with their passes more than they should.
"You have to cross at the right moment," he added. "We tried to force it too much and it didn't happen.
"I think it was stupid to do that because we delivered them too quick from too far out.
"The right moment was from Christian Eriksen in the first half to deliver, when he found the right moment, I think he found the pocket to deliver the ball to Cristiano (Ronaldo) at the far post. That was the right moment."
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