Having seen Pablo Barrios sent off, Atletico fought back from Iago Aspas' penalty to draw through Alexander Sorloth.
Simeone said afterwards: "I give the team a 10 out of 10. 90 minutes with one less player, a complete game. We gave few chances to score against a team that plays very well.
"The boys overcame an obstacle that presented itself, first with one less player, then with a goal that made us lose and they had the courage to keep running. I am very happy with the work of the players and it is an important step.
"The team played very well. The players became gladiators. Against Bayern Leverkusen, a team that plays well, and now against Celta, which is a similar team.
"They asked me what I thought of one to ten, and I said ten. They played ninety minutes with one less player, I had never seen that before. We held off their attacks, they had no scoring chances except the last one, they scored a goal from a penalty, which was a penalty. We dared to take the risk with what we had, it was an obstacle they put in our way and we managed it."