The Black Cats, with one win and two draws from their opening three Championship fixtures, fell to a 2-0 loss at home to Leeds United in Saturday's late kickoff.
"For 20 minutes we were dominant. We asked a lot of questions of them," he told BBC Sport. "I don't think Cooper knew too much about it when it hit him on the head and hit the bar - 70 seconds later it's in the back of our next. Those are the fine margins in a football match.
"From then onwards, I don't think you can fault the players' effort or commitment, but it was just that final ball that really matters, when you're trying to get back in to a game."
Sunderland, who had just one attempt on target all evening, return to action on Tuesday with a trip to take on Carlisle United in the EFL Cup.