Koeman told BT Sport: "A lot went wrong. Except maybe after the first 10 minutes, where he had a little better of the ball and it was more comfortable.
"Ball position was poor but most painful was in the first half - they showed more aggression, they showed more passion. That's really painful because it starts with that and then you need quality on the ball.
"I ask myself questions on what I was doing wrong against Tottenham, because it's not how I like to see my team. We can play bad football, we can miss chances, but the commitment and passion they showed in first half was much bigger than we showed."
Everton's next Europa League encounter is in a fortnight's time, against Apollon Limassol at Goodison Park.