Referee Stuart Attwell gave Bruno Fernandes’ goal on Saturday afternoon to make it 1-1 after the linesman’s flag had gone up when it was adjudged that the offside Marcus Rashford had not interfered with play.
“I can see that from the other side as well - of course it's a confusing moment but when you follow the rules he didn't touch the ball, he was not interfering and it's a goal,” he told BT Sport.
“We were happy at half-time but after half-time it changed, we were not proactive any more and just before I wanted to change it, they score.
“But then the spirit in the team is so huge, the belief is there that this game is 90 minutes, and we can fight back, and they believed they could turn it around.”
Ten Hag praised Rashford for scoring United’s winner after suffering what appeared to be a significant injury blow in the first half.
The United boss added: “Players have to be resilient - you get kicked in a game and obviously it happens and it hurts. But you have to keep going to get the right result, and deal with that painful moment even if it keeps being painful.
“That's what he did today and he gets rewarded for it, and the team gets rewarded for it. In top football you have to suffer and sacrifice to get the right result.”