Mike Phelan refused to blame Andrew Robertson after his mistake led to Manchester City eventually claiming a 3-0 win over Hull.
The hosts did well to stifle Pep Guardiola's side, even enjoying some good chances of their own before Robertson took Raheem Sterling's legs from under him before Yaya Toure opened the scoring.
Goals from Kelechi Iheanacho and a Curtis Davies own goal wrapped up the win, with Phelan admitting the error would be a learning curve for the Scotland international.
He told Sky Sports 1: "It was a moment of madness in a way.
"A young, good asset for the club has now got to learn his trade the hard way. You've got to concentrate and make the correct decisions. He got caught with a sucker punch really.
"He's young. His displays have been really good. Today he was terrific at times but those are the harsh lessons you have to learn as a young player.
"I'm not going to chastise a young player because he's a terrific prospect, he's a great asset and he'll be better for it.''
Hull had chances of their own before Toure's opener, with Michael Dawson's looping header cleared off the line by Bacary Sagna, leaving a bittersweet taste for Phelan.
"The effort was terrific,'' he said. "It was more than enough to get something more out of the game but elementary mistakes and lack of concentration against high-quality performers.
"You can't do those sort of things and we're in that sort of mood now where you get punished for every mistake you make.''
Iheanacho, who added another dimension to the City side when introduced off the bench, thinks Guardiola's side have turned a corner following three successive league wins.
He said: "I think we're getting our confidence back and into the winning mentality, so I think we are stepping up now.
"We are strong in the back and in the front now, scoring goals and getting the points. The next games we will be strong.''