Emery's side were 2-0 ahead as they entered the final 10 minutes, but the home side struck back to secure a share of the spoils.
"In a game in which we go 2-0 up, which we have controlled and that our opponents' chances were dropping, we have conceded two goals and finished with a draw," he told reporters at a press conference.
"We carry a big disappointment away because we have failed to keep our lead in the game. I blame it on being comfortable. We can only be guided by our feelings. It was a game to win and to sentence, but we go home with a point. Leading 2-0 does not guarantee a result because first we also have to keep a clean sheet.
"Yet I still believed that the team will take steps, that this is a backwards but in the general context we will move forward. Here was a day to be happy but in the end we fell underwater and ran out of breath."
Sevilla have not won away from home in La Liga since September 2012.