The Belgian made a string of fine saves but could not prevent Valencia's dramatic equalizer, though the Atletico boss praised his side's character.
Raul Garcia put the visitors in front in the first-leg quarterfinal and Courtois pulled off some smart saves - most notably from Sofiane Feghouli - to keep his side in the ascenancy until Helder Postiga headed in a dramatic late equalizer.
Simeone was thrilled with the young shot-stopper's showing, both on Tuesday and in the season as a whole, and admitted he was delighted with his side's efforts against a revitalized Los Che outfit.
"Valencia were brave and attacked us. We defended with pride and courage. We put in a huge effort. The result is important and the tie is now at 50-50 for each team," Simeone told reporters after the match. It's true that, after the goal, Valencia had two or three clear chances which our keeper did very well to save.
"Courtois played at his usual, very good level, and Raul Garcia is a great player.
"I'm proud of my players' commitment in all competitions, it's hugely valuable."
Simeone was impressed by the performance of Valencia under new coach Juan Antonio Pizzi and backed the side to be fighting for one of the four Champions League places come the end of the season.
"Valencia have very good footballers. They are a great team and they should be fighting for third spot," he added.