Julian Alvarez struck the winner for the hosts on Saturday.
Simeone said, "They are a tough opponent, who have gone 16 games without losing. They have a lot of fast players. We were quite organized in the game.
"They had Iñaki's situation, which Oblak stopped, and before us, Le Normand's, who couldn't finish off the ball almost under the goal. It was even. The back-and-forth didn't suit us. In the second half, the changes helped us, as did Oblak and Lady Luck with the ball hitting the post and the crossbar.
"I want to say 'thank you' to my players, because they are making an incredible effort and are working with enormous optimism and enthusiasm."
On Alvarez, Simeone also said: "When we knew that his arrival was confirmed, we were very happy because he was a different player, like Luis Suárez in his time. They are players who have a gift, who are special, like (David) Villa in his time. I am happy about his humility, his way of working, playing as the fourth on the left, waiting on the bench to come on..."