United went 2-0 ahead at the Optus Stadium thanks to Jadon Sancho and a Matty Cash own goal. But Villa fought back in the second half, first through Leon Bailey, and then a Calum Chambers header with the last action of the game.
Ten Hag said afterwards he was pleased with the first half performance on a difficult pitch in heavy rain in western Australia but delivered a brutal assessment of the second 45 minutes.
“We had a lot of movement behind the defending line, scored two great goals so we were 2-0 up at half-time and then our focus dropped,” Ten Hag said.
“It can be that the guys are tired but that’s not an excuse. They have to perform and it is what we didn’t do in the second half. In the first half we were really good.”
The heavy conditions did not help the flow of the game, but Ten Hag refused to look for an excuse afterwards and again blamed his players for not making it four wins from four on the tour of Thailand and Australia.
“It was the focus,” he said.
“I don’t want to make excuses about the pitch or weather. No matter what we have to perform.
“Football is a sport of mistakes and we have to decrease the mistakes. That’s clear but I have seen a lot of progress in these two weeks.
“In the first half I saw really good football, really controlling and dominating the game but we have to learn from what happened in the second half. It’s not possible that you go 2-0 and then throw it away.
“That’s what I just said in the dressing room, a drop of focus is unacceptable but to the season I’m happy because now I can tell them it cannot happen.
“We have to get out of the dressing room and back in your plan and your focus and back to your performance and that is what we didn’t do.”
Goalkeeper David De Gea might have done better with Chambers’ goal, scored after a Villa corner from the right, but Ten Hag refused to blame his goalkeeper.
“I have to see it back,” he said.